How do you help a tiny baby rabit to survive being separated from it's mom?

Born wild. It has teeth. Munched just a little on celery leaf and a bite of raspberry. Eyes open. No bigger than my fist. Already trusts. We just want to help it get bigger so it can finally fend for itself. Had loose stool over the night, as it did survive the night with us watching over it. I don't know if it still needs formula.