These things are amazing.  My son used them at Summer Camp and would wear them all day instead of shoes, sandals or boots.  If he wasn't in these he was barefoot.  Will out grow them before wearing them out.  Arch support? - a lot compared with flip-flops or barefoot.  Fit is hard to describe.  As stated, I 'think' they run a little small but if you can fit into them, they're still comfortable.  Not quite the same sizing experience of a regular shoe.  I have an adult pair and love them.  Takes a bit of self confidence to wear them, style wise, but worth it anywhere near the water.  Very best part - you have the support and flexibility of your two large toes and the others are protected as a trio.  Boating, especially sailboats, fast movement on deck will occasionally result in your little toe not making it past a shroud line or cleat.  Big time ouch.  I love the way these protect those toes as a group.  Good deck grip and great protection from sharp, bitty things.  Stays on yet no chaffing.  Don't collect much sand either.  Drains almost instantly.  Just don't spend the day in them w/o getting really wet toward the end or your foot smell when you take them off will knock you out.