Sometimes the attendants in places like this aren't empowered by management to use their own powers of analytical thought -- meaning, that particular person felt that they must follow the rules to the letter, or perhaps face getting in trouble. The situation they were facing could be something no one ever told them how to handle, which is definitely a problem in management of the place. Kids fall down and get hurt and they should know what to do -- jump in and do something about it immediately and forget about what's on someone's feet when there's an emergency!
Before you decide this is a terrible place and you're never going again, contact the owner (I think they're franchises) or manager and describe what happened. Be sure to explain to them about your physical need for shoes so that they'll get it. Find out what their policy is about injured children and blood clean-up. Let them know their employee at the time didn't know how to deal with it.
We've been to lots of indoor playplaces, Under the Sea included. This never came up when I was there, so I have no idea how any of them would handle the situation. I also have a problem being barefooted or in just socks, so I always bring slippers. I show them to the attendant and let them know I only wear them indoors at places like that and then no one ever gives me any trouble. The slippers have thick enough soles that my arches are supported, but they still look like slippers, not shoes.
Good luck and happy indoor playing, if you decide to give it another chance.
- Colleen