Jayapataka Swami: One time Srila Bhaktisiddanta Saraswati Thakura said, that he would indulge in sex life, if he knew that every time he was guaranteed to have a Krsna conscious child. That is why every time the child will be a pure devotee, that is not guaranteed. That is why we try. From the beginning, we want a Krsna conscious potential child. We pray to the deities, we get the blessings of guru, we do the garbhadana samskara. Then also, we have to bring up the child with love and affection. It is not an accident that they become a devotee! They may get some special association of a pure devotee, and the parents naturally feel that they are very successful, if their child becomes a devotee.  There is no sastra that says that if a child is not a devotee, then somehow it affects the parents. But the first five years, if the child commits any sinful acts, the parents have to take the responsibility. This was a curse given by a rishi to Yamaraja,so that this would be done in the universe. Because when he was a little child, Yamaraja poked an insect with a grass.