Be nice if you could have each of them sign a waiver of some sort saying that you are not responsible for their children as they are not in your care.

I ran into this at parks at my old location. Except it was other daycare providers. They would go sit on the benches away from the action chatting and not watching the kids. I would find myself in the midst of 15 or more children under 4, and found it too chaotic to monitor my group, while needing to aid the others too. I loved when our backyard was ready to spend most of our time there. We would still go to the parks at times I found others not to be there for variety, but had the back yard to retreat to.