K.T.
I work at a nature center and we get these calls all the time. Leave the babies alone. The mother will visit the nest as she sees fit. She will stay away as much as possible so as not to draw attention to the nest. If some of the babies die, that is part of nature. The reason why some animals have so many babies is because they know not all will live (think of rabbits). Please explain to your children that this is part of the natural cycle of things. Also if a hawk were to eat one, then the hawk lives for another day. Eventually the mother may kick the fledglings out of the nest. She does this to facilitate thier learning to fly, she did not abandon them, she will come down to feed them. Resist the tempation to take them inside your house. It is also a fallacy that the mother will abandon the babies if they are touched by humans. Especially for rabbits, the best thing you can do for them is to touch them; the mother will come back at night and, smelling your scent, will deem the nest unsafe and move the nest. This is only to be done if there is a threat to the nest, i.e. a dog or being mowed over.
I hope this helps!