I am the same size (11-1/2 W) and I got size 11. They fit great! Still have 1/4" extra in the toe and width is perfect for my 2E feet. Still brand new but the quality seems excellent.
I wear a man's size 7 and I ordered a size 7 .... they are true to size . I'm not sure about a childs size ... that might differ a little ... I not sure if they offer childrens sizes .
I bought a Large suit, being a 5'6", 180 lb., athletic male. It was slightly hard to zip, but comfortable. I suggest a male mediumfor this customer. My 8.5 shoe size foot measures 10" & the size 8 booty is 10.5". Since the upper is expandable & has a velcroclosure, I was glad I went with the smaller size for a close fit.
These shoes would probably protect against small pieces of glass, but large shards would be a problem. I wear mine in a pool with a very rough bottom. The pool used to cause small cuts and bruises, and I wore out two other pairs of boots before I found these.