Help for a baby mouse!?

i need help!!! i found a baby field mouse outside, it had 4 siblings but sadly they were all dead, i found the mother a few feet away, she was dead too. he seems to be the only one to have survived a horrible tragedy. i have never cared for a baby rodent before, though i have owned mice(they were all weaned). i have him in a small cage with his original nest and some ripped up tissue, i feed him goats milk with an eye dropper. also, his eyes and ears are still closed but he has some very short, velvety-feeling fur. any idea how old he is or additional info on how to care for him? please please help! i really don't want him to die:(