Nope, the one on the left in the picture is Clark, he was born a premie at 1lb 13oz. Tyke on the right though was full term at 8lb 3oz, Clark is 2, Tyke is 1, yet they wear the same diaper size.
We need to talk if you can get them out of diapers in a year. My son will be 3 in a few months and we can't get him even slightly interested in the potty.