Is Zakat obligatory upon the father or the mother for the children whose mother is divorced?

The father is obligated to pay Zakat al-Fitr on behalf of his minor children who are unable to earn, and their mother's divorce does not exempt him from this. As for the divorced wife, her ex-husband is not obligated to pay her Zakat al-Fitr if the divorce was irrevocable (ba'in) or if it was revocable (raj'i) and her 'iddah (waiting period) ended before the time Zakat became due.