If it were me I would have just given him back the cat when he first asked for it. A 10 and 14 year old should be able to understand that they changed their minds. Since you all fell in love with tha cat I would then go to a shelter and pick up kitten/cat and give it a second chance for a good life. If your shelters are anything like ours they are turning away animals because they don't have room for any more.