M.L.
Keep it very warm, we had this happen too, 4 baby bunnies, they only lived about 2 days, since it was over the weekend and the animal control wouldn't help us until Monday. Most vets wont see them unless they do the small animals (I know, I've worked for vets), but call your wildlife center. They will usually tell you to put the rabbit back... or pick it up on a weekday. Get to the vet first thing in the morning though!
this link will tell you all you need to know:
http://www.rabbit.org/faq/sections/orphan.html