What Is the Ideal Number of Kids?

The research behind how the number of children you have impacts parental happiness, parenting quality, and outcomes for your children

Apr 12, 2023

One of the most common questions I get on my Parenting Translator platform is something along the lines of “How many kids should I have?”. I understand why this question is so common— the decision of how many kids you have is arguably one of the most important decisions you make as a parent. That is, assuming you are lucky enough to have this choice— many people are limited by fertility, age, financial constraints, and other factors that make the choice for them. The research on this topic is also very limited since, of course, researchers cannot randomly assign parents to have more or less children and the parents that choose to have smaller families are different in many ways from the parents who choose to have larger families. However, for parents who feel torn about this decision, the advice to “do whatever feels best for your family” may leave you feeling lost, so in today’s newsletter I will review the limited research we have on this question and help you to consider some important factors.

If you are trying to make this decision for your own family, please pause before reading this newsletter and imagine that the research provides a clear answer to the “ideal” number of kids. What are you hoping the answer will be (1 kid? 2 kids? 3 kids? More?). The answer that you are hoping for might be more important than any research study.

But first a BIG announcement…

Personally, I have been thinking about this decision a lot because I am currently pregnant with my fourth child! I have not “officially” announced pregnancy on social media or in any other forms yet so you, as a loyal subscriber of he Parenting Translator newsletter, are the first to publicly find out that I have a baby girl due in August 2023. My children (who are currently 7, 5, and 2.5 years old) are very excited and we all couldn’t be more thrilled.

Finding out I was pregnant (with an audience, of course)

However, unlike previous pregnancies, the response I have gotten to announcing this pregnancy is not “congratulations” but more along the lines of “Why on earth would you have so many kids?!?” Honestly, we did not base this decision on research or even rationality, but our very unscientific intuition that “someone was missing” and our illogical love of babies. But the questioning of this decision has pushed me to really dig into the research on family size and the “ideal” number of kids.

So what does the research find is associated with family size? Is there really an ideal number of children?

Parental Happiness

Research is mixed as to what number of children is associated with the happiest parents. First, an older study found that one child may be ideal in terms of the parent’s happiness. In this study, researchers found that having the first child was associated with increased happiness of both parents while having a second child had little impact on the father’s happiness but actually decreased the mother’s happiness. In fact, each additional child was associated with decreased happiness for mothers with three additional children (four children in total) having such a negative impact that it negated the positive impact of the first child.

A more recent study found that having the first child was associated with increased happiness before and after the birth for both parents and that this occurred to a lesser extent for the birth of the second child. However, having a third child was not associated with increased happiness and instead was associated with decreasing happiness over time (see graph below).

Source: Myrskylä, M., & Margolis, R. (2014). Happiness: Before and after the kids. Demography, 51(5), 1843-1866.

Another study found this pattern of decreased happiness with more children across 86 countries. However, this study examined the factors that may influence this relationship. First, this effect is very dependent on age (see graph below). Parents age 30 to 39 do not show decreased happiness with more children, but rather no difference in happiness with more children, up until 4 or more children (which is associated with decreased happiness). Parents age 40 and older actually show increased happiness with each child (up until 4 children which again is associated with decreased happiness). This difference in age occurs regardless of income, partnership status, health status, country, or what age you have children. This likely reflects that as parents and children grow older the children become less “work” and usually require less time and financial resources. In other words, although having a lot of younger children may negatively impact your happiness, this effect fades as you and the children age.

Source: Margolis, R., & Myrskylä, M. (2011). A global perspective on happiness and fertility. Population and development review, 37(1), 29–56.

This effect may also depends on how much support you have. The researchers found that people in countries with more public support don’t see as great of a decrease in happiness for each child.

Does the gender of the children matter? Research finds that having one child of each gender (that is, at least one boy and one girl) is not associated with increased happiness, but that a firstborn son may be associated with more happiness in fathers than a firstborn daughter.

TRANSLATION: Research suggests that parental happiness may decrease with each additional child after the first child. However, this may not be true for parents who are 30 and older or who have more resources or support.

Other Impacts on Parents

Mothers report that having more children is associated with more anxiety related to parenting (concerns about your children’s wellbeing) and role captivity (feeling trapped in their role as a parent). However, mothers also report that having more children did not seem to impact their joy in the parent-child relationship or their sense that parenting has given their life new meaning.

Research finds that women who have three or more children are more likely to have a lower salary and that this persists throughout their lifetime. For women with fewer than three children, their salary and status seems to rebound as their children get older. Research also finds that the more children that women have, the more likely they are to drop out of the workforce.

TRANSLATION: Research suggests that having more children is linked to more anxiety related to parenting, feeling “trapped” in your role, and being more likely to drop out of the workforce or earn a lower salary. However, it is not linked to joy in the parent-child relationship or parenting giving your life a sense of meaning.

Parenting Quality/ Resources

Research finds that the more children that parents have, the less resources they have for each child —including financial resources, time, supervision, and affection (in the research, this is called the resource dilution model). In other words, there is some evidence that, when the quantity of children increases, the quality of parenting decreases including less language and time for each child.

Language

Research finds that any children born after the firstborn receive less language input from their parents than their firstborn sibling. This is important since one-on-interactions with adults are known to promote language development. However, more recent research suggests having an older sister may counteract this effect (presumably because older sisters talk more to their younger siblings).

Time

Research consistently finds that parents have less time to devote to each child as they have more children. One study found that parents spend 20 to 30 minutes per day of quality time more with a firstborn child than a second child of the same age from a similar family (this adds up to 3000 hours of quality time with mother and father between the ages of 4 to 13). Research also finds that the more siblings a child has, the less time parents spend in caregiving activities with each child. This does not seem to be improve with greater socioeconomic status (in fact, fathers of higher socioeconomic status spend less time with each child when they have more children than fathers of lower socioeconomic status).

Affection & Home Safety

Encouragingly, research finds no difference in how much affection parents give each child or how safe the home environment is with each additional child.

TRANSLATION: Research finds each additional child may get less time and language input from parents, yet additional children seem to still get the same amount of affection and supervision from parents.

The Impact on Children

So having more children seems to be negatively related to parent wellbeing and parenting quality but does having more children impact the outcomes of the children themselves?

A large study from the National Bureau of Economic Research in the United States found that having more children was associated with a decrease in the cognitive abilities (translation: IQ) of each child and an increase in the behavioral problems shown by children. Children from larger families also completed fewer years of education and earned less as adults. Each additional child lowered the average educational years of the older children by 0.13 years. However, the researchers also found that children with mothers who scored higher on a test suggesting they were in higher socioeconomic classes did not seem to have the same negative associations with having more children.

A study including over 1,000 5 to 6-year-olds in France found that the more older siblings that a child has, the lower they score on measures of language and verbal IQ. Interestingly they found no relationship between number of older siblings and nonverbal cognitive abilities.

Another study found that children from larger families were less likely to attend private school and more likely to be held back in school. The relationship between education and family size is likely related to family resources (both parent time and money) because closely spaced children are more likely to drop out of high school or not attend college than siblings spaced farther apart

TRANSLATION: Having more children is associated with lower cognitive scores (particularly for verbal skills), increased behavioral problems, and less education in children. Yet, these associations are likely related to family resources.

Are There Any Benefits?

The research on larger families seems mostly negative but there has to be some benefits to children in having more siblings, right?!? Research finds that having at least one sibling may be related to improved social skills and that having multiple siblings is also related to a child’s theory of mind skills (translation: perspective-taking). However, it may be the quality of the sibling relationship not the number of siblings that predicts children’s social skill development.

Having more siblings may also help to protect children from stress. Research finds that children are less likely to show a negative impact of divorce when they have more siblings.

Siblings may also benefit children up until old age. Research suggests that elderly people with contact with their siblings report higher life satisfaction.

TRANSLATION: Children may benefit from having siblings including improved social skills, protection from stress, and life satisfaction.

Are All of these Negative Associations Related to Resources?

These studies largely find negative outcomes associated with having more children. However, could this all be related to resources (money, time, energy, and other parent resources)?

One study found that parent resources explain most (or even all) of the relationship between number of children and educational outcomes. In this study, they looked at both interpersonal resources (how often you talk to your child, knowing your child’s friends, having educational expectations for your child) and financial resources (having a computer and educational objects in the home, engaging in enriching activities outside of school, saving money for college). This finding suggests that number of children may not matter as much as whether parents have both the interpersonal and financial resources to provide for the children they have.

Research also suggests that the impact of family size on children’s education may be minimal in countries like Norway that provide paid parental leave and subsidized high-quality child care. Interestingly, other research finds that having more children seems to have the largest negative impact on happiness for parents in the United States, where very little support is provided for parents.

Another study found that the negative impacts on parental well-being were eliminated when they controlled for financial resources and partner status. In other words, more children does not decrease happiness for families with enough financial resources or two-parent homes. Instead, parental well-being may decrease with each child due to the financial strain of having more children. This quote from the study authors really sums it up:

“Children then raise happiness as long as they do not lead to difficulties in paying the bills.”

TRANSLATION: The negative impacts of having more children seem to relate to the resources that the family has. This research suggests that before having more children you should carefully consider the financial resources and other resources (such as time, patience, etc.) that you would have to devote to another child.

Limitations

This research is very limited due to the unavoidable methodological issue that you cannot randomly assign families to have more children or fewer children. As a result, all of this research is correlational, meaning we can only find associations between the number of children and the outcomes and we do not know if they were caused by the choice to have more children. The parents that choose to have larger families are different from those who do not in many important ways that can’t always be controlled for in research. Researchers have tried to eliminate this problem by looking at spontaneous twin births (since parents did not choose to conceive twins) and people who have more children because they want to have both genders (for example, a family that has three boys and only had a fourth child in hopes of having a girl). For example, in one study that used these methods to control for making the choice to have more children, there was no relationship between family size and children’s education. However, these methods of course are not perfect either— twins may also be more stressful for families than singletons and people who choose to have more children to even out gender composition may also be different than people who do not.

Another limitation is that there are many factors that are very important to parents and families that have not been studied by research. For example, having a smaller family may make it easier to travel or engage in other activities that are meaningful for your family, while having a larger family results in built-in babysitters and playmates. Research also has yet to examine how family size impacts child development, child mental health, or a sense of belonging or social support.

Overall Translation

The decision to have another child is a very personal choice that is based on many unique factors that are difficult to research or even quantify. This a decision that each family must make on their own considering all of these different factors. Even after spending days writing about the negative associations with having a larger family, I am still happy with our decision to have four children, simply because it is what feels best for our family.

It is also very common to have fewer children than you would have wanted due to factors outside of your control such as age, fertility, and financial constraints, particularly in countries like the United States that provide little support for parents. This is a heartbreaking situation to be in. Allow yourself to grieve this loss of what could have been, even if you rationally understand the benefits of having a smaller family.

However, the research does suggest that parents may want to consider whether they have the resources to really provide for another child (both financial and other resources such as time, energy, and affection). However, because most parents cannot increase financial resources, time, or energy, if you want more children or already have more children, it may help to focus on consciously providing more attention and affection to each child and providing a community of support for each child, because these resources are also invaluable to children.

As with many parenting decisions, research cannot make this decision for you. Think back to the number of children you were hoping that research would suggest is “ideal” before reading this newsletter and think about what number makes your family feel “complete.” These intuitive feelings may be more important than any research finding.

Expert Review

All Parenting Translator are reviewed by experts in the topic to make sure that they are as helpful and as accurate for parents as possible. Today’s newsletter was reviewed by Rebecca Berlin, PhD. Dr. Berlin received her PhD from the University of Virginia School of Education and has served as a special education teacher, home visitor, child assessor, autism specialist and school administrator. She has conducted research on the teacher-child interactions, as well as play and story based interventions for improving social skills and classroom quality. She currently serves as the Executive Director for the Parenting Translator Foundation.

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