All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
If the share of each of the orphan children reaches the Nisaab (i.e. the minimum amount liable for Zakah) – the equivalent of 85 grams of gold – and a whole lunar year has elapsed on it, then Zakah becomes due on it. The guardian of the orphans or the one in charge of them is responsible for paying their Zakah. It is noteworthy that Zakah may not be given without intention, which is one of the Zakah-related conditions as held by the majority of scholars. Thus, the guardian should intend the paid money as Zakah on their behalf.
Accordingly, if the probate court which administers the wealth of orphans, is the guardian over them, then they should fear Allaah The Almighty and pay the Zakah due on their money, should the share of each one reach the Nisaab and witness the elapse of a lunar year. If they do not do so, it is their responsibility before Allaah The Almighty and there is no blame on the mother. When the children reach legal age and receive their money, they will have to pay the Zakah due on all the years that passed.
Allaah Knows best.