Nestlings have few or no feathers, and if found on the ground, they need your help. These baby birds are too young to leave the nest and are unable to fly. 

Step 1:  If you have spotted a nestling that isn’t injured, shaking, or weak and you can locate the nest, use clean or gloved hands to place the bird back into the nest quickly. 

Step2: If you cannot spot a nest, you need to create a surrogate nest. It can be made with a carton box/plastic basket. Ensure that it’s well-padded with paper, of non-slippery kind. Otherwise the bird’s legs could spread out sideways and become deformed.

Step3: Keep the bird in a sheltered place away from cats and dogs but close to the area where you found the bird. Chances are that the parents will continue feeding them. Continue monitoring the bird for a few hours from a distance, to see if parents turn up.

Step 4: If you see the parents not coming, then you need to keep the surrogate nest warm (keeping a small hot water bottle under the tissues) and call for help. The nest should be kept in a closet or another warm, dark, quiet, and safe place away from people and animals. DO NOT OFFER ANY FOOD.

Step 5: Get help – Call ARRC (Animal, Reptile Rescue Centre) at 81050 61005. This really works. We have gathered these inputs from people who have actually saved nestlings of Kite in Whitefield. The people from ARRC came and took the nestlings with them. After a month they came back with the birds and kept them at the original location. The parents came back and acknowledged the same. It was surreal!

The above article also has some inputs from the PETA website.