As many cars are not large enough to fit three car seats in one back row, many families desiring a third child might be faced with having to buy a minivan or large SUV to accommodate.
"These laws significantly raise the cost of having a third child, as many regular-sized cars cannot fit three child seats in the back," the paper states.
"These laws are certainly well-intended, but end up having big negative effects on birth rates that we think policy-makers might not have properly considered," Solomon told CNA.
While Solomon and Dickerson wrote their paper in 2020, the issue was addressed years ago by author and journalist Jonathan V. Last, who wrote about car seats in his 2013 book on American demographic challenges, "What to Expect when No One's Expecting."
"While the car seat is objectively pro-child, it is also vaguely anti-family," Last wrote in the book, noting the problem of many families having to upgrade their vehicle to accommodate a third car seat.
His conclusion, however, was that car seat policies present another burden to growing families, but do not significantly affect birth rates.
"The role car seats play in depressing fertility is minuscule-so minuscule as to be immeasurable," he wrote. According to the paper by Solomon and Dickerson, state mandates effected a 0.73 percentage point decline in the probability of giving birth among women with two children in the age range of car seat laws.
However, Last wrote, "it does add costs to the price of children," and the state laws "didn't make life any easier for parents with lots of kids."
The fertility rate in the United States hit a record low in 2019 of 1.7 children per woman of child-bearing age.
The fertility rate has declined since 2007, when it was above-replacement level at 2.12 children per woman.
Most of the negative effect of car seat policies on births has come in this period, since 2008, the paper by Dickerson and Solomon claims. Regulations grew stricter since the mid-1990s, with state age limits for seat regulations soaring upwards.
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"By contrast, if current laws had applied over the whole sample, we estimate there would have been a further 350,000 fewer births," the professors said of the current regulations.
Matt Hadro was the political editor at Catholic News Agency through October 2021. He previously worked as CNA senior D.C. correspondent and as a press secretary for U.S. Congressman Chris Smith.