What is the ruling on a mother selling to her children for money?

It is not permissible to sell children or any other free person, by consensus. Islamic Sharia (definition) has absolutely forbidden the sale of a free human being, because the human body, alive or dead, is not considered property. This is one of the manifestations of Allah's honoring of the Children of Adam, as stated in His Almighty saying: "And We have certainly honored the Children of Adam and carried them on the land and sea and provided for them of the good things and preferred them over much of what We have created, with [definite] preference."