A colleague of mine, who is a Christian, married a Muslim man.
When she became pregnant they agreed that if the baby was a daughter, she would be raised in her mother's faith, and if a son, he would be raised as a Muslim.
As it happens, the child was a girl. They have not had any children since (firstly, my colleague was coming to the end of her child-bearing years when they met; and secondly, the marriage didn't last)