2. Borrow or Foster

Children (and some adults) tend to have a rather rose-tinted view of a pet being all fun and no hassle, if they haven't dealt with the realities of pet ownership before. You may be able to cure them of their puppy obsession by borrowing a pet from someone else; after dealing with the mess and effort, they might quickly lose interest. You could also foster as a way of showing them the commitment involved.