I bought a size 10-11 for my 5 year old (normally a size 10 shoe) for school.  Luckily his little brother (3) needed a pair too because they were way too small.  My 3 year old has a size 9 foot and the size 10-11 fit him beautifully.  I'd suggest ordering up a size.  Quality is nice and the foam foot bedding looks comfortable.