My mother's sister has two children. One is eleven and one is seven. They are both being given an unusually religious education. (Their mother, who is Catholic, sent them to a prestigious Jewish pre-school, and they seem to be going through the usual Sunday School bullshit.) I find this disturbing and want to proselytize for atheism to them. Any advice?

ETA: Their father is non-religious. I don't know why he's putting up with this.