Maybe the babies are Cowbirds in a sparrows nest. Cowbirds are notorious for not building their own nests and laying their eggs in other birds nest. When the babies hatch the cowbird is typically bigger than the rest and will eat most the food. The poor parents trying to feed them will run theirselves ragged trying to feed the Cowbird while their own babies die from starvation. A lot of time the Cowbird baby will even knock the smaller birds or eggs out of the nest.

Mabye the mother of the nest has realized these are not her babies and has abandoned the nest.

I need to find a picture of Cowbird babies online to see if they look like yours.