I’m not anywhere near an expert, but I’ve tried my best to save a few orphaned babies from the hay fields.
Often they die. It sounds terrible but they’re just really delicate and hard for humans to care for.
I fed mine either warm milk (not too warm, just a little over room temp) or kitten formula (not sure if that was the right thing to do, it was a last resort). The other thing to watch out for is to make sure they’re clean. Like chicks, their butts can get all nasty, as well as their mouths. They eat a lot, like every hour or two, and they can’t eat much at one time.
Apparently the mother mouse would lick or massage them after feeding, to keep their digestive systems moving? I’m not sure about that, it’s been a long time and all my information came from my neighbors and the internet.
Probably the best thing to do would to bring them to a wildlife rehab center. In my experience, it’s more trouble and heartbreak than it’s worth to try it yourself. But by all means don’t take my word for it, I definitely didn’t know what I was doing and didn’t have the right setup. Good luck with whatever you choose to do! I hope everything goes well!