Babies end up on the ground for a number of reasons. Sometimes an overeager nestling literally jumps out of the nest in its attempt to be fed first.
Predators attack nests and babies fall to the ground.
The parents will not reject their Baby or harm it in any way if you touch the babies. Try to reunite the family as soon as possible. Uses round plastic container, the approximate size of the nest. A margarine tub makes an excellent nest. Put lots at holes in the sides and bottom for drainage and ventilation.