Work out how old the mouse roughly is. Sex them. Do they have their eyes open? They open their eyes at about 12 days old. If they have their eyes open but they are wobbly walking and not jumping around, they haven't been weaned on solids just yet. In which case, kitten milk is a necessity. They must be fed this milk every hour. You must sex them as males and females personalities are very, very different. So in order to work out what you need to keep them happy, have a quick look. If they have their eyes open and they are very steady and they like to jump, they need solid foods. Such as, special pellets for mice and a few little bits of veg for them. If you have a container to keep them in, make sure it has a lid and it's not a barred cage as they can squeeze through very tiny holes. They can also jump very high so make sure there are no holes on the lid big enough for them to squeeze out of, but enough to allow them to breathe. They like to borrow and hide themselves in awkward places. Make sure they don't get bored as they will start biting their tail out of bordem. Good luck!