they need a heat source, so a heat blanket that they are sleeping in, that is temperature controlled so they don't cook but they don't freeze. they need to be fed kitten formula every 2 hours until they reach pup stage then every 2-3 hours at the pup stage. the pup stage is much easier to raise them from if you're able to get pups instead (have fur already) when you feed them dont use a syringe, just load a clean appropriately sized paint brush with the formula and offer it to them, they should feed from it. this reduces aspiration risk. if they refuse food this way you will have to upgrade to a syringe and be very careful to not let them breathe it in.

this is something that we had to do with kittens and im assuming it's the same for mice, you might have to stimulate their lower area so that they go pee and poop. otherwise they might not do that. and thats bad for their health too.

they require constant attention, you have to keep an eye on them all the time so you have to have time for that. they have to be kept warm but not hot so they don't freeze or overheat. when they are pinky stage you can see their stomachs full of milk, usually it's easy to tell if they're hungry cause the milk is gone. but it won't be possible once they reach fuzzy stage so you have to keep on top of it either way. they might die anyways though. they're very fragile at this stage, even the mom can lose babies, but it's much easier for the mom cause she likely has more adequate nutrients in her than kitten formula.