If the mom bunny is doing a good job caring for the baby, this might not be needed. But if you have any doubts you might want to step in and care for the baby yourself. I searched in google and this is what I found...

http://www.mybunny.org/info/newborn.htm

http://www.hrschicago.org/newbabyfr.html

I'll try to find more. You might want to call your vet and just see what they have to say on the situation. Good luck and keep me posted!