Well, they had (very vaguely referenced) "rules" to make sure it was safe, and I'm sure in general the adults were fairly closely involved even if they let the children have the final say in everything. So you couldn't MAKE them create an accessible playground, but you could certainly encourage it. And you could always make sure there were disabled children in the group, to get a more full range of opinions.

I mean, that's a lot of bother, and I'm not saying they're terrible people for not doing it (If they didn't). But they could have.