Instructions
Make sure the bunny has been abandoned and is not simply lost by finding a nearby nest. A rabbit nest will be in the ground and lined with fur and grass. There may be other bunnies there. It is not uncommon for a mother rabbit to leave a nest alone for a period of time while she looks for food, so a nest full of baby bunnies that appears abandoned may in fact not be. A good way to determine if a nest has been abandoned is to place two sticks across the entrance of the nest in a cross shape and check back in a couple of hours. If the sticks are gone, you can be reasonably sure that the mother has returned and has not abandoned her babies. Place the lost baby in the nest and it should be fine.
See if the baby is old enough to survive on its own if you cannot find a nest. Once a rabbit is the size of your fist, has its eyes open and ears that stick straight up, it's old enough to survive on its own. Release it into a wooded area with plenty of undergrowth. You should look for a white blaze on its forehead; this is a good indicator that it is old enough to survive without your help.
Try to help the baby only if it is smaller than your fist, its eyes are closed, and its ears are back. These are indicators that it is too young to survive on its own. Assuming there is no nest to be found, keep the baby warm by holding it in your hands or shirt gently but securely enough so that it doesn't jump away. It will be small and weak enough that being dropped will kill it. Place it in a box lined with cloth from T-shirts or sweatshirts. Don't use shredded newspaper; it can have toxic materials. Call a wildlife rehabilitator immediately so the bunny can be relocated to a shelter.
How to Save a Wild Baby Bunny
Every year people attempt to save wild baby rabbits that have either been abandoned by their mothers or have gotten lost when they strayed from their nests. Saving these young animals can be difficult, especially since they can be so delicate that people's efforts often end up killing them. Finding lost or abandoned bunnies occurs often enough that you may end up finding one yourself.