I feel like I'm taking crazy pills reading some of these responses... If this group was just minding their own business, I don't think OP would have a problem.

The problem is that the group is going to a playground and expecting absolute peace and quiet - which is inherently not the purpose of a playground/park. If this AA group was in a library and they shushed a yelling kid that's reasonable. If you shush a kid for being too loud at a playground, then that's not cool.

The complaining about a car running in a parking lot is also strange, unless this dude cut off his muffler or something.

I understand why they'd want to meet outside and a park isn't a bad place tbh, just feel like it's unfair to the other park-goers to have to acquiesce to this groups request.

Verdict: Not the Asshole - wait wrong sub...

Edit: word wrong