How to help baby rabbits

Rabbits will not abandon their young if a human touches a baby.

 I found a nest of rabbits and I don't see the mother. 

Mother rabbits do not stay with their young. They visit their nests infrequently (usually at dusk and dawn). To make sure that the mother is tending her young, take four long pieces of dental floss and lay them over the nest in a "tic tac toe". Check the nest in the morning. If the floss has been moved (significantly), the mother has in all likelihood nursed the infants. If the floss has not been disturbed, contact a rehabilitator for advice. 

I uncovered or disturbed a rabbit nest. 

If a nest has been uncovered, remove any of the rabbits that might have been injured. Try to restore the nest to resemble its original design, then replace the uninjured rabbits. To make sure the mother is feeding the young you can perform the same test described above. 

I found an orphaned rabbit 

Rabbit mothers nurse their young then quickly leave the nest so as not to attract attention to their nest. Young rabbits also begin to leave the nest and return at a very young age. 

Typically if you have to chase the rabbit to catch it, it doesn't need help. 

A dog or cat has found the nest. 

If possible the pet needs to be keep away from the nest, rather than kidnapping the young. Young rabbits will be on their own three weeks after birth. Young rabbits have a much greater chance of survival being cared for by their mother.