The reason that you seldom see baby pigeons is that they do not leave the nest until they look like very much like adults. So if you recognize it as a baby it probably needs your help.
Pigeons make devoted parents but if a baby pigeon is taken from the nest or falls from the nest before it is fully fledged its parents will not recognize it and won't feed it.
A baby pigeon will look a bit like a duckling. It has a long flat beak, yellow fuzzy hair, fleshy nose wattles , a short tail, no feathers under its wings, big feet and short legs.
These pigeons are in early development. They do not leave the nest until they are 35 days old.