It can be very annoying/dangerous in a sports centre though- I had this the other week with my DD's (preschool) swimming lessons. It was half term so some older siblings had been dragged along.
There were 2 that spent the whole half an hour charging up and down past the seats, climbing on the barrier, and going in/out of the viewing area repeatedly. Bear in mind the set up is that there is a single row of chairs and a waist high barrier between the seats and the pool. The barrier is close enough to the chairs that I could stretch my feet out and touch the barrier if I wanted and to allow someone to pass you have to tuck your feet under.
There were other, younger children that were sitting nicely, watching the swimming, chatting, some had brought along things for the children to do. If all of the children had been allowed to run like these 2 (as my niece wanted to) then there would undoubtedly have been an accident.
Add to that, the barrier was making a very irritating banging noise as the children climbing along it, it was disturbing me, so must have been putting off the children in the pool too!
It's a sports centre, as well as the sports facilities there's a cafe just outside of the pool area, and a outside play area too, if the children really couldn't sit still for whatever reason, there were more appropriate areas for them to go to. Or they could just not go to swimming lessons while it's half term?