Sounds like the mother is moving her babies. It can take a while so she may come back for it or something could have happened to her. I'd just keep watching for a while. If not, it will need to be bottle fed. I bottle fed my cat, Leonardo. He was about 10 days old though. He looked like Popeye the sailor with one eye almost open. There is a powdered milk available for orphaned babies. The vet could tell you more about it. Good luck.