I let JW family babysit my girls, ages 6 and 3.
My rules are simple, I don't want them talking about or correcting my child's viewpoints on holidays, birthdays, etc. I also don't want them talking about anything negative such as the big A.
If they would like to talk about God in a positive manner, pray before meals, etc, I'm fine with that. But, if my daughter is scared in any sort of way or repeats something in a negative way, there will be a huge problem. My daughter repeats everything.
My family respects my wishes and so I haven't really had a problem.
The only thing I do have concern with, is that we will be celebrating holidays so I'm sure my daughter will talk about it to JW relatives. That could pose some huge problems but I guess that's just life. Maybe I'll get d'ffed and they won't have anything to do with us.
You really can't protect your kids from unforeseen occurrences, just deal with it the best you can and teach your children proper coping skills. Also, try to make other friends with kids so your kids aren't also so heavily reliant on just a few people surrounding them...