You should pay the Zakah due on the money of your mother under your custody and should pay the Zakah in cash. You are permitted to buy clothes with it and distribute them to the poor when it is better for them. And it is impermissible to give Zakah to her children or her grandchildren, because
the Zakah of the ancestor is not permitted to be given to his/her descendants and vice versa [i.e. the Zakah of the descendant is not permitted to be given to his/her ancestors].May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.