YWNBU, but I would probably have made passive aggressive tuts or something 
.
As an aside - since this thread has gone this way (!) I don't let my 17 month old on the equipment alone - not because he can't. But so he doesn't beat up your kid, snatch their toy and make them cry, or just completely disappear off the radar. There are too many exit points for him to escape from 
.
Toddler DS is something of a Houdini. There are several soft plays in our area, and pretty much all of them he can escape from out to the carpark. He hasn't made it outside yet, but only because I am constantly stalking keeping tabs on him. I've got to him past the gate that hasn't been closed from fucking knobheads other parents coming in or out. He could easily escape. Also, he moves so fast, and is below table/adult height. I can't get to him fast enough sometimes as others are in my way. He honestly has no sense of danger or fear. He has never stopped and looked around for me.
I regularly can be found legging it after him, removing him from behind counters and kitchens also - which is dangerous in itself.
Sorry, but if he gives me so much trouble when I am actively following him around, can you imagine what would actually happen if he was supervised from a distance. If I couldn't actually see him, I'd shit myself he'd got out.
On Saturday he disappeared between the pretty packed out tables. He didn't appear again, I started going after him, couldn't see him or find him. I headed towards the exit, because that's my first port of call when he goes missing - to stop him escaping.
Anyway. Yeah. I stay with my toddler for many reasons. Until he has any sort of understanding it will stay that way. He appears to have very little understanding of anything yet, other than 'clap hands', 'ta' (give me that dangerous object right now little child), and 'all gone'. He snatches toys - because he hasn't understood that isn't acceptable yet. And he won't understand it unless I stay with him, remove said snatched toy, give it back to other child, remind him that we don't take things off others, and apologise if the other parents are there. You know, setting a good example to him. Teaching him right from wrong.
So forgive me for going on the equipment with him, but really, it's in your childrens best interests.
I'm pretty sure my older child didn't need this level of supervision, but then we didn't use soft play til he was 3. We've been going since toddler DS was 7 months old and crawling. I am assuming by 3 he will have mastered some sort of control over his behaviours. Perhaps not. We shall see!