https://mikvah.org/article/breastfeeding_and_jewish_law
A general outline of the laws of breastfeeding. A woman should consult her own Rav for any clarifications.
Small children (under 6-7) are exempt from Jewish law. Making breast milk kosher isn't exactly neccsery, but it makes things much easier (how to keep it, making sure it won't get mixed with other foods by mistake, what happened if it does etc.) The neat part is that breast milk isn't considered milk accordingly to Jewish law, so it can be drunk with/right after/before eating meat (otherwise forbidden). This means a person can, and I know at least one who actually did, add breast milk to their coffee after eating meat.