Before baby mice open their eyes, they're too young to be weaned. The mother mouse will feed them milk. If the babies don't have a mother or have been abandoned, they'll need to be fostered or hand-fed, or they won't survive.
Baby mice are adorable. I love them! You can tell the difference by searching around for their mother and if you can't find her wait in the shadows. If she still doesn't return it means they have been abandoned. Save those mice!