There are those who enjoy mice as pets, but in my opinion they're not the best pets for kids. I ve raised them and found them to be nervous, skiddish little animals. If there are more than one in a cage, I ve seen them attack and even kill each other. Mice also have a stronger odor than that of hamsters, gerbils, and rats, so they need to have their cages changed more often. Mice can be kept as pets, but may not be the best choice.
Rats make wonderful pets for any child who is old enough to care for it.
In raising rats I ve never had an aggressive one. They actually seem to enjoy human company. They spend more of the day awake than gerbils and hamsters do. They seem to be more relaxed and slower moving, which makes it easier for a younger child to handle them. Rats are clean animals as long as they are provided with good clean bedding.