Will a Muslim who has become senile benefit if his children give charity from his money before his death, knowing that he had previously refused to donate all of his money out of consideration for his heirs? And does their action equate to giving the money after his death?

As long as the father is alive, his money may not be disposed of without his permission. If he becomes senile, his case is referred to the Sharia (definition) court to issue its ruling on whether or not to place him under interdiction.

If the court rules that he is competent, his permission is required to dispose of his money. If the court rules to place him under interdiction, the guardian may not dispose of his money except in ways that are beneficial to him, with caution. He is not permitted to give charity from his money, because a person under interdiction cannot validly donate his money.