I'd teach your kids to ask questions that embarrass theists. Most theists are more afraid of embarassment than they are in converting.

An example question might be... "Today if a man said he heard voices and sw things that nobody else could see or hear, we say he was mentally ill." However if it happened more than two thousand years ago we call them prophets. In ancient times the mentally ill were said to have been "touched by the gods". So, isn't religin based ont eh writings of mentally ill persons?

Teh above actually might be mroe fun if mentally ill were substituted with "crazy" which is more to a kids understanding and vocabulary.

Anyway, load your kids with a few embarrassing inquiries and takign them to church events wont' happen so often anymore.

How old are your sons?

I'd try being direct and polite about it if you are that bothered. And/or talk to your kid's about your position and ask them how they feel. You wouldn't want to ruin their relationship with their cousins because of your sister. She might still push it on them or be passive aggressive about her beliefs a bit but she shouldn't take them places you don't approve. If they are just going over there less than once a month I don't think it's enough to brainwash them if they are intelligent. Might not be a terrible experience learning about the phenomenon of weird religions from a generally outside perspective... Or keep them on Sundays... Sounds like my mom, in her mind what she is doing is Noble and the right thing so try not to take the BS too seriously.

It should be noted that when her kids come to town, I don’t deny them of their rituals or impose my opinion on them .