I love the shark reef. There is no fee and your 10 year old will be able to go in with you if they can swim (just make sure they can swim without kicking their legs as you are asked not to do this.) When I went in I took an underwater camera (one of those disposable ones) with me to take some pictures of the fish and sharks.
Have fun.
I remember wearing a life jacket thing but that was a few years ago. The recent pictures I have seen they don't seem to wear one. Does anyone know for sure? I would love my 7 year old daughter to do it, she can swim but I remember it being deep. I would be happier if she had some sort of flotation device.
As Dana mentioned, you are asked not to kick your feet. This is due tot he fact that since people are looking generally down, they will not see you ahead of them and MAY swim up to you. If you are kicking, there is a good chance of kicking them in the face.