When I worked at Old Navy (years ago) the toddler sizes had less room for diapers. They were thinking toddlers were being potty trained. This may have changed by now but I specifically remember watching a video about it long ago.
We have found 2t is taller which is what R needs. He's 2/3T in tops but he can wear 18month pants because he has no hips or tushy. We did get some 2T skinny jeans and they actually stay up. we just have to do a slight cuff because they are a little long
Re: 24 months/2T?