My daughter is 4 now, and wears a 10.5 shoe.  She wore the size 2-3 all summer, and still fits them, so I bought 2 more pairs to get her through her weekly swim lessons.  I like her to wear these so she doesn't slip on the pool deck and/or get fungus infections.  Because they are so soft they don't hinder her swimming at all or bother the instructor (they won't scratch up your skin like a hard soled shoe would).  I would have given it 5 stars if the sole of the shoes lasted longer.  After a few wears, the spot underneath the big toe wears down easily and creates a hole, hence the reason I'm buying 2 pairs at a time.  My daughter puts these on JUST BEFORE she gets into the pool for her lesson, and we take them off right away, so it's not like she's walking/running around in them.  I also do wash them in cold water then line dry. The soles just aren't durable enough.  When my daughter outgrows these in the Spring I will have to search for another brand as they don't make them any bigger, but so far have had no luck finding something similar.  The "water socks" for preschool age and older all seem to be made of tougher material, for actually walking on sand, etc.