Onesies are so misleading. I mainly put my little guy in onesies, but I decided to put a pair of shorts on him... 12 months were too small!!! He just turned 8 months! While he fits 9 and 12 month onesies, they stretch, so I think he is truly 18 months. Poor little guy was squished in his shorts, I had to take them off. Looks like we will have a lot more clothes to pass on now!