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 wrinkled and empty looking, mom has been lost to a predator or a car, etc.  She won't 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 mom does not return, take the babies to Wildlife Rehab in Fenton on Gregory Lane.  The number is 636-343-6200.   This particular facility in Fenton has a good cottontail survival rate.