Yes, they do. The crotch strap should be less than 5.5 inches from the seat back to the crotch. The idea is to keep the child from slouching in the carrier. You can always put something in the extra space of the strap to keep the baby straight such as a blanket or diaper rolled up for cushion. You also do not want the strap from the bottom to the top to come into contact with the ears of the child. The distance for this strap should not be more than 10 inches for the best effect for preemies.