New swimming pool shoes

Since the old ones are becoming too small, I bought a new pair for Greta. it is "2-3 years" size... How come people say a child's feet are changing so fast, if Greta uses her shoes for mor than a year now and they still fit? Anyway, these ones are like 4 cm bigger than Greta's feet. :-)) Can't imagine a 2 year old with such a big foot (but I know, actually, they do exist)