Mice are very social with members of their own kind, and females will do especially well in a group. Males can be kept together if introduced at a young age—if introduced when adults, they will fight. If you plan to keep several males together, however, be certain that you’ve provided enough room. Do not house males and females together, since mice breed quickly—and often—with large litters.
You can keep three to four mice in a ten-gallon aquarium with a wire cover. There should be several inches of bedding. Use either aspen or hard wood shavings or reprocessed paper products. Avoid cedar and pine shavings at all costs, as these may cause health problems for your pets.
Don’t forget the furniture! Provide small boxes or flower pots for your pets to hide in, and cardboard tubes for your mice to chew and run through. You can also add a tree branch for them to climb on. Most mice will enjoy running on an exercise wheel, so be sure to get yours one. Make sure that the wheel has a solid surface without wire rungs, so your pets’ tails cannot get caught while running. Ladders for climbing and PVC pipes for tunneling will also be much appreciated by your bright, active pets.
Plastic habitats—the kind designed for hamsters—will also work for mice. However, since mice are smaller than hamsters, you may need to put small branches in the tubes so the mice can climb up and down these “steps.” Keep in mind, however, that these plastic habitats can be more difficult to clean. The ASPCA does not recommend that you keep your mice in a wire cage made for hamsters. These models may have bars spaced too far apart to keep mice inside. If a person can stick his fingers through the bars, a young mouse could probably sneak out as well.
Pet mice are social and active critters that need a variety of toys to chew on, as well as items that provide opportunities for exercise. A good quality wheel will provide lots of exercise (get a quiet wheel as they love to run at night). A variety of toys to climb and chew on will also help keep pet mice active and healthy.
Most mice will become quite tame given time,patience and perhaps a little bribery. At first, allow the mice time to become accustomed to their new environment. Once the mice are calm, start spending more time around their cage and quietly talk to the mice to get them used to your voice. As the mice become comfortable or curious with your presence, start offering some favorite tidbits (try millet or sunflower seeds) by hand, and once the mice are taking treats from your hands, they may start walking on your hands, or you can start trying to pick them up.
When picking up a mouse, it is best to try scooping it up by cupping your hand under the mouse (but do not squeeze or tightly grasp the mouse's body). If holding a skittish mouse, you can try holding the base of the tail with one hand while supporting the mouse's body in the palm of your other hand to prevent the mouse from jumping off your hand and possibly injuring itself.
Similarly, you can hold a mouse by the base of the tail and gently lift a bit to allow you to place your hand under the body to pick the mouse up. It is vital that you only grasp the base of the tail gently and very close to the body. If you hold further down towared the tip of the tail, you may break the tail off or the skin may come off the tail.
Be careful when holding mice as a relatively short fall can cause injuries. It is best to hold the mouse just above your lap or some other soft surface in case it falls or jumps.
If you need to pick up an mouse that isn't yet tame place a cup (or paper tube covered on one end) on its side in front of the mouse, and gently herd the mouse into the cup, which can be used to carry the mouse. It is also possible to pick up a mouse by the very base of the tail if you have no toher choice. This doesn't really hurt the mouse, but it is stressful for them and probably uncomfortable.
If you are going to allow your mouse time outside the cage, you will need to mouse proof the room. Ideally, keeping them contained in a large shallow plastic storage box, small wading pool or some other confined space is the best option for keeping the mice safe and sound. Even then, you should make sure there is nothing in the your mouse can get into and hide (such as the underside of the couch, or very narrow space between furniture), or any way the mouse can escape on you. Make sure all electrical cords are out of reach, and that there is nothing else that could harm the mouse including poisonous plants. Remember, mice can be pretty hard to catch so make sure they don't get away on you!
I hope I helped you with your problem. Mice are wonderful pets and I am glad that you care so much about their wellbeing! Good Luck!