We had mice problems in a couple of rented houses. I even found a fresh poop in my baby's bed. I was able to keep them out of her room with the use of cottonwool balls soaked in peppermint essence or oil. I put these under all the furniture and found no more mouse evidence in her room.
I didn't like killing them so got humane traps. One night we were amused by the sight of a mouse sitting on top of the trap - a cage with a hole in the top that the mouse can't get back out of once inside. This mouse was using it's backlegs to hold onto the top of the cage, while lowering it's self down the hole, stretching a front leg through the wires around the hole and pulling the bait directly under the hole. Smart mouse.