You can gift your self-acquired property to your minor grandchildren by executing a registered gift deed. The mother of the children, or even yourself, can be appointed as the guardian. Under Muslim Law, this is known as 'Hiba' and has specific requirements, including acceptance by the guardian. If the appointed guardian dies, the court will appoint an executor. While such gifts are generally permissible, they can be challenged under certain circumstances, such as coercion or lack of proper possession.