Mother cottontails stay away from the nest so they don't attract predators to their babies. Mom will normally nurse the babies twice a day around dusk and dawn when the least amount of predators are around. Do not disturb the nest.
You can check to see if mom is returning by putting several strings across the nest in a tic-tac-toe sort of pattern and then checking it the next day. If the strings have been moved, then mom is coming back. She scratches away the covering of the nest while hovering over it and looking like she's just eating grass to fool anyone watching. The babies nurse from underneath. She then scratches the covering back over the nest and nonchalantly continues grazing as she moves further away from the nest; again to fool any predator watching. She doesn't know how to put the strings back into place properly so they'll be all messed up.
You can also tell if mom has been there (if it's necessary to handle the babies,) by looking at their tummies. If they are wrinkled and empty looking, mom has been lost to a predator or a car, etc. She normally would not desert her babies. If the tummies are rounded, then she's still around somewhere. If the tummies are rounded and you have handled the babies, you can put one tiny drop of vanilla or cologne on their foreheads to confuse the human scent. If you put too much then the predators and ants will smell them. Baby bunnies have no scent to attract either. Baby bunnies are normally in the nest for about 4 weeks before going off on their own.
If mother rabbit does not return, do NOT attempt to make them pets. They have different needs than domestic rabbits and generally die in captivity. Take the babies to Wildlife Rehab Clinic. They have moved to High Ridge at 1864 Little Brennan Road, phone: 636-677-3670. They have a good cottontail survival rate.