I can understand a kid asking for a giant rat as a pet. What I can't understand is any parent that says "OK". The Gambian pouched rat (Cricetomys gambianus) is a size most people would associate with a cat, not a rat. It's a rat that can be a metre long.
This large African rodent ("pouched" as in cheek pouches for hording all that rat food) has cost the taxpayers of the United States a fair few dollars to satisfy the "needs" of a few rat lovers that want to get one up on the Joneses. In 2003, a recently imported giant rat carried monkeypox into the USA, infecting prairie dogs, who went on to infect their new owners. Dozens of cases in the US midwest were traced to prairie dogs from Phil's Pocket Pets in Illinois. Monkeypox is a pretty serious disease, akin to mild smallpox, so naturally the US Centers for Disease Control (CDC) took the outbreak pretty seriously. The disease has about a 10% mortality rate in Africa.