What should a mother do whose "Mongol" child moves her during prayer, and is anything incumbent upon her?

It is permissible to carry a child during prayer, whether it is an obligatory (fard) or supererogatory (nafl) prayer, as is their clinging to the worshipper. This is evidenced by the action of the Prophet (peace and blessings be upon him) when he carried Umamah bint Abi al-As while leading people in prayer, and his statement about al-Hasan ibn Ali: "But my son mounted me, and I disliked to hasten him until he had fulfilled his need." There is no difference between obligatory and supererogatory prayers in this regard. The claim that his action (peace and blessings be upon him) was unintentional is baseless. As for a child moving their mother during prayer, it is permissible as long as it does not lead to turning away from the Qiblah or excessive movement.