Rats are designed to eat just about everything... cream of wheat included. Our rats eat mostly leftovers and disgusting stuff they dive for in the kitchen trash. Just about all human foods are good for rats, but just like humans, rats shouldn't just eat any single food all of the time.
Fuzzy Rat ate meals with her human family and we found that every day she mixed up her diet. One day she preferred meats and the next it might be grains and veggies... Naturally candy, cake and cookies were always preferred, so it's not something you should make a standing option of. But you shouldn't do that with kids either.
As part of a diverse diet, cream of wheat is fine.