Letters of His Divine Grace A. C. Bhaktivedānta Swami Prabhupāda
Regarding your question: “What is the correct sexual etiquette for a strict Grhastha; and what is spiritual family planning?” Unless one wants to beget a child, there should not be any sex life. The best thing is to forget sex, but it is not possible immediately or all of a sudden, especially in the Western countries where sex life is so liberal. So under the circumstances, one should try to have sex life only for children, not for any other purpose. Spiritual family planning is that one should be determined to train up children in Krishna Consciousness. According to Bhagavata, the spiritual family planning is that one should not become a father or one should not become a mother, unless he is able to maintain their children to the extent of liberation. It is the duty of the parents to see that the children are growing luxuriantly not only materially, but spiritually also. So spiritual training should be given from the very beginning. Kaumaram acaret prajna—In the Srimad-Bhagavatam, Prahlada Maharaja has instructed that spiritual consciousness or Krishna Consciousness should be taught to the children from the very beginning as they are given education from early childhood.
[Letter dated 24th August, 1968 to Dayananda and Nandarani]