My daughter is 18 months and just now got into a size 4. Every kid is different.
My 16mo old daughter has been in a size 4 for a few months now she is almost ready for a size 5. Her feet are so fat though! Lol I have to get her wides to even get her foot in!
I have the hardest time feeling his toes in his shoes so Its hard to tell if they're too small
My boy is 15months and he's in a 5 1/2-6