The first time I saw that sisters were asking this question to scholars online, I laughed. It has never crossed my mind that breastmilk could be considered najis. But after some thinking, I realized that there are many valid reasons to ask this question. Though breastfeeding is not sexual, it is an intimate act of feeding. And living in a culture where breasts are appreciated more for being erotic than for feeding infants, it is understandable that people will have this idea. Another reason people may have this doubt is that breastmilk is another body fluid like blood and semen which do compromise wudu. However, scholars unanimously agree that breastmilk and breastfeeding does not break the mother’s wudu. See the following links for more info.