Rodents should be kept in bared cages, not aquariums. They need the fresh air and ventilation. Aquariums trap the odors and fumes and will slowly poison your pet. I would get a female to avoid the aggression of a mature male.Ah. Most parents give the kid a cage pet, keep it in the child's room, and let the child handle it whenever he wants, without supervision. It is more at risk than a kitten -- a kitten can scream loudly, and run away, is less fragile to begin with, and interacts with the entire family, thus gaining the attention of an adult when there is a problem. I've seen a lot of little creatures crushed and killed or injured by small children, or left without water, but kittens growing up in families with very little kids have done fine.
I think a ten gallon is too small for rats. They're active and clever and need play space. I'd get two males. They're smellier, but they grow bigger and are generally more cuddly and slower moving. Take your kid to handle some rats before buying them -- some people are allergic to them. Myself included, which is a pity because they're really wonderful.