Jez:
Good point. The child is getting hurt and being discriminated against, for no good reason. I'm not even aware of anything in the literature that speaks of the innocent children of DF'ed ones having to be shunned. Maybe they wont let the kids go round, because of exposure to adults, but that's a different matter from the schoolyard. It might be good if the teachers were aware of the situation, so they can monitor it, even if they don't initially do anything about it.
Confused:
If the relationship was never that great with the parents and you are well clear of the JW's, it seems there's nothing to lose. Warning them in a letter might cause them to think.
There is, however the potential embarrassment to your "sweat pea", though.
I remember what it was like when my parents went to the school to sort out some bullies, when I was a nipper. I was mortified, and although the bullying stopped, the taunts and cold stares didn't.
The chances are the JW kid is embarrassed, too. Kids often have a way of thinking things through that adults don't. It could be that they'll settle their own differences.
Fairmind:I agree with your conclusions, but not necessarily the reasoning that arrived at them.
Are you really as neutral as you think you are?
IMHO the children come first, above any public spectacle, etc.