These rompers were so great! My son needed a helmet to fix his flat head and he wasn't going to a daycare facility where the employees have experience taking helmets on and off. He was staying at home with my mother-in-law and so I wanted to find something that she didn't need put over his head. My son is on the larger size, in the 96th percentile for weight and 75th for height. He was 4.5 months old when I got these and I ordered the 6 to 9 month size and they fit him great. They were a tad big at first but not too big where he couldn't wear them. He is 7 months now and they still fit him. Very happy with my purchase!