Is it permissible to use money collected from families and saved for students until needed, then return it?

It is not permissible to use money that is a trust (amana), because it is considered a betrayal of the trust. Allah Almighty said: "O you who have believed, do not betray Allah and the Messenger or betray your trusts while you know [the consequence]." And the Prophet, peace and blessings be upon him, said: "He has no faith who has no trustworthiness, and he has no religion who has no covenant."