JustAKitten
"5 when you're comfortable with the risk. I'm comfortable with a level of rough housing and so once DS can speak and is slightly older, I have no problem.
But I also wouldn't moan if another child fell on him. If that bothers you, then you need to supervise."
You are wrong about this - it is reasonable to expect children to follow social norms at soft play the same way you expect adults to follow traffic rules or any other laws in wider society.
It is not up to me to supervise my 6 year old (say) just in case you have decided to let your 3 year old (for example, if that is the age at which you become comfortable with the risk) break the social contract all the children are implicitly aware of at soft play and put my perceptive, considerate child at risk of being upset that he has accidental hurt your oblivious, careless, thoughtless, self centred one.
The only reason anyone can back off and be hands off when their children are playing around other children is because the unsupervised children have learnt how to play considerately and co-operatively.
You sound as though you have no intention of teaching your child to be thoughtful aware of the social contracts that enable society to function, on a micro scale at soft play and perhaps on a macro scale either...
That's on you, not everyone else.