Like... They have a really fatty top part? DD already has big feet for her age (16 mo, was a 5 by 12 mos, now 5.5). Her feet are also wide-ish (tho she fits into M sneakers). But I think b/c her feet are slightly wide (or they just fan out like a duck), plus that top part of her feet are SO meaty, I can't stuff her in most shoes unless they have a big opening!