Is it permissible to allocate a portion of Zakat to deserving children within the sister's family, or is giving Zakat to the mother sufficient?

It is permissible to give zakat to your sister if she falls under the description of the poor and needy, and if her husband is unable to provide for her and her children. Indeed, it is more deserving, as it is both charity and maintaining kinship ties. It is permissible to give the payment to her husband, as he is the provider, or to your sister and her adult children if their father is unable. It should be given to adult daughters unconditionally due to their inability to earn, and to an adult son if he is unable to earn. As for minor children, their guardian (father) receives the zakat money on their behalf.