Shortly after I bought my two first "female" mice from a pet store, I realized one was pregnant and the other was definitely not a female. After that, it was really difficult to remove the young males before another female got pregnant, so for a few years, I had a constant stream of mice families. It was actually really fun!
The pregnancies only take about a month, and the babies are fully grown in about a month. The babies were very cute, and the mothers are good to the babies (I never experienced any of the horror stories you hear about the mothers eating the babies or anything like that.)
I kept my mice in a 20-gallon glass aquarium with a mesh wire top. The bedding was recycled fibers geared toward small rodents, which I thought would be softer for them compared to the wood chips. The other supplies include a water distributor, food bowl, a wheel, and food. The initial start-up costs, including the mouse should be less than $50. For houses and "toys," I used old tissue boxes (or any thin cardboard box) and toilet paper rolls. They were very cheap, and the mice loved to chew on them. When they got dirty, I could just throw them away and replace them. I changed the bedding about once a week (or when it started to smell), and I did a deep clean of the aquarium with bleach and water about once a month.
The Pros of Owning Mice They are very cheap pets to buy and maintain. The amount of space they occupy is so small that they would fit in apartments or kids' rooms. They are very active and curious which makes them fun to play with and watch. They are easy to entertain (like I said, I just used thin cardboard scraps most of the time) and feed.
The Cons of Owning Mice Mice are naturally nocturnal, which means they will be loud and noisy at night. I recommend buying a plastic wheel that is silent so that you don't have to listen to the metal ones squeaking all night. Their cages do require pretty regular clean-up or they will get smelly. Depending on the personality of your mice, they may not be as trusting or friendly to humans. In my experience with my mice, about 25% were very friendly, 50% were sometimes friendly, and 25% were very scared of me.