We've been attending a playgroup for a year and most of the time we've really enjoyed it. There is a boy there let's call him Billy whose GM takes him to the playgroup. Billy often comes over knocks over DS2's tower, or shoves DS2 and the other boys and runs off immediately (I think hes trying to get them to chase/play with him?). The boys then chase Billy (often all giggling like it's a game) but sometimes there is a scuffle or playfighting as the boys retaliate. Billys GM has started coming over to me randomly to make a nasty comment about how the boys play. Billy once got a small bump on his arm. GM made a huge fuss even tho she didn't see what happened and blamed DS2. I've recently found out Billys GM is telling mutual friends that my DS2 is violent and I don't supervise enough. Just to be clear when Billy cried I was there before Billys GM asking the boys what had happened and making it clear that they must be nice to Billy and I always step in to stop any poor behaviour I see DS2 doing. Meanwhile Billy's GM doesn't seem to even notice that Billy is provoking the boys and he is never reprimanded for pushing tower over etc. It is possible that Billys GM doesn't even see the provocation, it happens in a flash the minute she turns her back.
At the moment I just step in every time I see this group of boys getting boisterous tell them to stop and then forget about it (they're just toddlers after all) but I'm getting upset but the nasty comments and the things being said about me and DS2 and that Billy is getting away with all his provocation whilst DS2 and other boys are labelled violent. I think I need to get better at handling these kind of things as there will always be parents/situations like this so that's why I'm asking WWYD? Any top tips on dealing with these kinds of situation?