I took 8 and 5yo to one (Wandsworth) recently. They had a whale of a time and I was nearby.
However - they were just bouncing on simple rectangles, plus ds hurling himself into a bouncy wall next to his, dd jumping off a springboard into the foam pit. The areas set up like a skateboarding park for older kids looked much more dangerous and the staff were concentrating on those, telling kids off frequently.
If I thought my child might want to try a somersault, then I don't think I'd want them doing that without a qualified teacher (not just me) supervising.
My advice is if you go, do not try copying small kids by jumping into the foam pit from the springboard, as adult weight squashes the foam so much you can't step on them to get out, so there were loads of adults stranded like beached whales until other parents helped drag them out! Dd managed to queue up again and jump and get out before I got out once, and it was exhausting!
We'll go again, but I won't take dn too as he would immediately try to somersault and is the kind of kid that invariably is bleeding within a minute of getting on a bouncy castle.