Nickerson and Solomon find that when a woman has two children below the car seat age, her chances of giving birth that year decline by 0.73 percentage points. This represents a large decline, as the probability of giving birth for a woman age 18-35 with two children is already 9.36% in their sample from census data. By contrast, they do not find significant effects of car seat laws where car-seat-related crowding is unlikely to be an issue. For instance, there are no significant differences in birth rates when the woman has only one child total of car seat age, or two children total where only one child is required to be in a car seat. The effect is also concentrated in households where there is an adult male in the household, increasing the likelihood that both front seats are occupied by adults.