Zakāt is wājib on the father or mother for the value of the jewellery which he or she bought and kept [in advance] for their son or daughter’s wedding which is still in their ownership and has not been given to the child as yet.
If they have given it to the child and it is now in the child’s ownership, zakāt is not wājib as long as the child is non-bāligh (immature).
After the child becomes bāligh (mature), zakāt becomes wājib [on the child] after the passing of one year provided that the conditions [for the wujūb of zakāt] such as [meeting] the niṣāb (minimum threshold) etc. are fulfilled.
References:
The cause for this is that he must be the owner of a productive niṣāb for one complete year. [Darr Mukhtār, Zakariyyā 3/174.]
The conditions for its wujub are sanity, maturity, Islam, freedom and ownership of niṣāb. [Bahr Raiq, Karachi 3/202, Fatawa Mahmoodiyah, Dabhel9/376, Shami, Zakariyya3/179, Fatawa Mahmoodiyah, Dabhel 9/339.]
Kitabul Masail Vol.2 Pg.220