A:AnswerI don't know the measurement size but should be fine for a 9 year old. I've used it while running and training dogs. I'm also using it this summer on a disney cruise and roller coasters.
A:AnswerWorks just fine in water and is even washable. To use the floaty back door you need to use extension links or the camera is only gonna point down. Other options might be the head piece or a mount on the jet ski
