Another vote for crocs!
We've worn them in WDW twice - no blister problems and no complaints from the kids about feet hurting either. Easy on and off, stay dry, no laces to fuss with, and can comfortably wear them wither w/ or w/o socks - on cooler evenings it can keep those toes warm to wear w/socks. Even DH has a pair that he brings to wear around the pool.