The Rabbis afforded great importance to nursing a newborn baby, which, as has been proven by modern medicine, yields numerous health benefits. For example, during the first several days after birth nursing provides the infant with colostrum, which has been shown to help protect children from various allergies and diseases. Mother's milk itself has likewise been determined to provide a child with important health benefits. Therefore, a woman who is able to nurse a child should not forego on this opportunity, even if bottle-feeding is more convenient.
The Shulchan Aruch (Yoreh Dei'a 81:7) presents the guidelines as to when it is no longer permissible to nurse a child. He writes that a healthy child may nurse until the end of his fourth year, and a sickly child is permitted to nurse from his mother until after he completes his fifth year of life. After this point, it becomes forbidden for him to nurse just as it is forbidden for older children and adults to nurse directly from a woman. The Shulchan Aruch adds that after twenty-four months have passed since birth, if the child stops nursing for a period of seventy-two hours, the mother may not resume nursing the child, unless some health risk is involved. Chacham Ovadia Yosef rules accordingly, in his work Halichot Olam (vol. 6, p. 229).
Therefore, a mother who still nurses her child after the first two years must bear in mind that if she leaves on a trip and will thus be unable to nurse the child for seventy-two hours, it will be forbidden for her to resume nursing upon her return.
Summary: Halacha encourages mothers to nurse their babies given the health benefits involved. A healthy child may nurse from the mother until after his fourth year, and a sick child, until after five years. After two years, however, a child who stops nursing for seventy-two hours may not resume nursing unless a health risk is involved.
