Super small, but definitely watertight!
The hole was waaaaaay too small for my daughter.  It definitely didn't let water in, but she said it was so tight it was painful and I had to work so hard carefully taking it off that I was afraid I'd pull her cast off!  My daughter is 12 years old and is small for her age.  I ordered the adult version and I hope it isn't too big. This would be perfect for a very small and/or young child, but not for a child that is older or heavy.
Rating: 2 stars