I admit the Islam would be a little more difficult for me because there's a possibility that one of the parents could be sending/taking the child to a place that practices or encourages radical Islam. Admittedly the parent could be taking the child to a "Christian" church that advocates bombing abortion clinics, too, I guess. But I probably wouldn't have a problem with either parent exposing this child to their respective religions as long as the child wasn't showing discomfort or confusion about it AND it wasn't altering her body in some way or doing something permanent to her that she could not back out of later when she is old enough to make her own decision. Her father just taking her to church seems rather innocent and not something that is going to permanently scar her in some way, as far as I can tell.