My three kids over the years had just about everything in the order of small animals.
The most fun were either the gerbils or the rats.
If you go the gerbil route, try using an aquarium filled about 1/3 full of a 50:50mix of peat moss and potting soil. Slightly dampen the mix, pack it in and bury a few larger rocks or bricks to give them a challange. The kids loved watching them tunnel and the mix absorbs the smells well. Make sure you have a secure lid as the jump very well.
For the rats, I built a large wire frame condo with multi levels that keep them busy, boy rats are docile and don't wander away from kids while being held. The little girls on the other hand love to wander and have to be watched....
Never really had a biting problem, but keep after the kids to have clean hands before going near.
Whatever you choose, enjoy their company.
