Aw, baby mice are EXTREMELY cute as they start to grow and get fur, but yeah, they will reproduce really quickly -- one of mine figured out how to get out of his cage and into the separate one that housed his sisters, very clever.
My favorite mouse experience as a kid was investigating our neighbors dumping something on the front lawn and discovering that it was a nest of wild brown mice, with fur, but with their eyes still closed. My and my sister were kind of horrified that they were being abandoned away from their mother so gathered them up and introduced them into a cage with a female pet store mouse we had. Within a brief period she had washed them all and collected them inside a plastic tub and made a new nest. The next day she was nursing them! She somehow developed milk?! As they grew they were much faster and more timid than tame mice so we released them in a field when they could eat dry food. Their foster mom ran ragged trying to keep up with them until then. She tried so hard though, and got them to adult mousehood :).
