These run a little small, so for my just-over-two daughter (who does have large thighs) I bought the 3T size, which is working out great. These are perfect for her, because she sometimes has a little #1 or #2 come out before she can stop it and get to the bathroom. these aren't so great for a full-on, it all comes out-type accident, but we're lucky that we rarely have those anymore.