Who has to pay Zakāt?
Zakāt is due on a Muslim who has reached the age of puberty, is of sound mind, and owns wealth at or above the niṣāb for a full lunar year. In the Hanafi school a child's wealth is generally not subject to Zakāt. The other three schools hold that it is, and a guardian pays it on the child's behalf.
Where this comes from
Zakat Made Easy, Mufti Faraz Adam: the position this app follows, used with the author's permission.