But twins are unexpected. They are a shock to the system, one that people only have a few months at most to prepare for. Parents with twins will have less time and money to spend on each child, so you can look at families with twins to see what happens as a result of the children getting less resources:
So what does it mean for an older brother when Mom and Dad come home for the hospital with twins? What's it like to be the younger sister of twins?
First, you get less computer time. Frenette finds that, even after controlling for family income, education, and myriad other factors, having twin siblings reduces the number of computers per child by 14.1 percentage points.
Second, you are less likely to be enrolled in private school — youth are 4 percentage points less likely to in private school when there are twins in the family, all else being equal.
Third, parents are less likely to save money for their children's post-secondary education in families with twins.
And the impact of fewer computers, less private school, and less saving for post-secondary education on children's academic performance is…not much.
Fifteen year olds from families with twins do no worse than other children in international standardized assessments of reading achievement. If anything, they appear to do slightly better — but there are too few families with twins in Frenette's sample to know whether the difference is statistically significant.
As a parent, I find these results encouraging. Even if your resources are stretched, and you can't do everything you've planned for your kids, they might turn out just fine anyways.
There is a lot of evidence that shows that, once their basic needs are met, the life outcomes of children have very little to do with how much time and money is spent on them. There is not really much need to work so hard on raising children.