We have a very different situation, OTWO, as you know.
We are atheists, both my wife and I, and we are responsible for raising our grandchildren for the past 8 years now. [Hence the reason your thread title caught my eye.] My daughter, though out of the picture, incarcerated and unlikely to ever gain custody again - vacilates between religious/non-religious opinion. Our approach has been to allow freethought within our home [as would be expected by humanists/secularists I suppose]. We do not throttle discussion of religion - though we strongly encourage thoughtful consideration of matters before taking a stand for any supposed ideology without logical proof thereof. We do allow the children, on the rare occasion in which they petition, to attend church with the neighbor kids. I suppose we have an agenda there too, though unintentional, of allowing them to see for themselves the silliness of religion.
But - and this is BIG BUT - if either of them ever wished to attend any religion that we have determined to be high-control/cult-like - the answer would be a sound NO. And we would discuss the reasons clearly and logically with them - but the answer would not waver. We have absolutely poisoned the well for them regarding Jehovah's Witnesses - they will never listen to those people. Or at least I can not imagine they would.
I am not interested in killing their free will - but I am telling it like it is - there is no point in the next generation making the same mistakes as the previous one.
For those curious as to how this affects the mother's view - well honestly, since I am raising her children due to her own lack of interest in being responsible, and I have full legal rights to do so - I am raising them as though they are my own. And I fully expect that we will raise them until they are adult [the oldest is nearly 13 now, and mom is still behind bars - once she is released, and IF she flies straight - she might be in a position to seek custody in 3 or 4 years - and that is unlikely to be honest from what we know.]
But, if we were a typical family - if the grandkids visited us, we would never foist our strong opinions on them unwillingly or without parental consent. I believe those Jw/cult types that do so are completly out of line. If I were a parent with little children, and had Jw parents who would do that - I am sorry, but those parents would be denied access.
Jeff