Find a thin eyedropper, one of this medical devices used in administering eye drops and other things. Warm up some milk in the microwave, so it's a little bit warmer then lukewarm, but just a little bit. Feed the mouse with this, to to start out with. It was on your kitchen floor? I wonder how it got there, you must have mice in your walls. Any cats in your house? They could have moved it. Make it a nice house/nest by using maybe an old shoe box. Use newspaper, old cloths/rags, and maybe some types of grasses. Create a nest for your mouse to fill comfortable, cozy, and at home in. Try and find some type of incubator light, but I'm pretty sure anything would work, such as maybe a light for reading that clips onto something and the stand is bendable; anything that gives off heat, one of those red incubator lights. This is so the mouse won't die of cold, because the mother isn't there. Feed your mouse often, she/he is growing. When she gets old enough wean her from the milk and start feeding her mouse food from the petshop and other things, maybe some veggies; carrots, etc. Buy her a small cage equippted with one of those vacuum water bottles that goes on the side. Use wood shavings. Talk to your local animal control or wildlife refuge about letting your mouse go or not, by this time it should be relatively tame. I do not know if it could survive in the wild, because it hasn't learn how to scavenger on it's own, it has turned into a pet. You may have a small and furry friend for the rest of your life, so when and if you decide your going to care for it, make a wise decision. You don't need anything too complicated to care for your baby mouse, and nothing expensive; remember, simple things will work. I hope this helps and if you have any questions contact a local wildlife reserve in your area who specialize in this kind of stuff.