My husband passed away and my children`s money is currently being held in trust in guardianship court. Is it obligatory to pay zakat on it or not? My son is four years old and my daughter is six.

All praise is for Allah, and may peace and blessing be upon the Messenger of Allah, his family, companions and followers. To proceed:

As long as your hands are tied and you are not free to dispose of this wealth, you are not required to pay zakat for it. That is because one of the conditions for paying zakat is "full possession" (tamam al-mulk). The meaning of this term includes the ability to have the property in your possession, to have sole property rights over it and the ability to dispose of it freely. I do not find this in the likes of your situation; and Allah Almighty is more exalted and more knowledgeable.