Ruling on zakaah on money in a charitable fund

A colleague of ours died (may Allah have mercy on him), and there is no one to look after his children after him except Allah. His colleagues set up a fund to collect donations, so that a monthly allowance can be given to them. Part of the agreement was that if it is possible to spend from that fund on other charitable causes, that would be done. But in fact, the donations are only used for this family. The money collected reached the nisaab (minimum threshold at which zakaah becomes due) and one year has passed. Is zakaah due on it, or is it like a waqf or charitable fund on which no zakaah is to be paid?