Many people feel compelled to act when faced with a baby bird on the ground. The small creature seems so helpless and vulnerable that the first impulse is to scoop it up and place it back in a nearby nest or take it home to rescue it. In the case of young robins, as well as most other baby birds, people need to be aware that while being on the ground is bad for a nestling, it is a necessary part of a fledgling robin's development. Therefore, people should be acquainted with differences between nestlings and fledglings.
Look at the feathering. A very small bird with few to no feathers or with only downy feathers is a nestling. A young robin whose lower breast is red and whose body is fully feathered including tail feathers is a fledgling. Fledgling robins are often on the ground because they leave the nest and spend a considerable time on the ground while they are learning to fly. While the baby is on the ground it is under the close supervision of its parents who feed it several times every half hour and teach it how to hide from predators.
Observe how it moves. If the young robin seems weak and can barely move, or if it lays in the grass and seems shaky, it is most likely a nestling. If it is hopping around on the ground and fluttering about, it is a fledgling.
Listen to the bird. Nestlings make peeping sounds. If the young bird is chirping loudly, it is probably a fledgling calling to its parents. The chirping is not a sound of distress. It is used to allow the parent birds to locate the young bird in order to feed it and protect it.
If you believe that a bird is a nestling, and you know where its nest is located, place it carefully back into the nest. If you think you are dealing with a fledgling, observe it for a half an hour or so. The adult birds should reappear. If they do not, contact a wildlife rescue centre, whose personnel are trained in caring for young birds.