Since Cottontail rabbits 'nest' in a small depression in the grass they are often disturbed by cats, dogs, children, or the occasional lawn mower.
If you have found a rabbit's nest with babies in it, it is important to watch to see if the mother comes back to feed her young. Eastern Cottontails nurse their young in the morning and at night. These are the only times when the mother can been seen at the nest. If the babies are alone in the nest this does not necessarily mean that they are abandoned. Please do not remove the babies from the nest unless they are injured, the mother is dead, or they are in danger. If you must remove the babies, please take them to your local wildlife rehabilitator.
In general Eastern Cottontails are very hard to hand raise due to the stress caused by human contact.