Often overlooked in favor of their smaller cousins, these gentle rodents actually make great pets for kids. They rarely bite, they love to play hide and seek, and they'll squeak with excitement when their humans put in an appearance.
Since they prefer to live in groups, consider adopting two female guinea pig. (Two males will be prone to fighting, unless they come from the same litter, and a male/female pair will result in lots of tiny guinea pigs.)
Guinea pigs also provide good practice for responsible pet ownership. If you're thinking about getting a bigger pet somewhere down the road, for example, longer-haired varieties are good preview for dog or cat ownership, since they need to be groomed daily in order to prevent tangles.
We've covered mice and guinea pigs, but what about rats? Read about domesticated rats on the next page.