You may already have seen newly fledged young pigeons but didn't recognize them. They look much like adults, but younger nestling pigeons are more difficult to see. Adult pigeons build nests in hard-to-reach places, such as covered crevices along building ledges, in the nooks and crannies of building beams and rafters, or in hidden-away places under bridges. You can find these birds nesting just about anywhere in the urban environment that resembles the caves and sea cliffs of their natural environment in Europe, the Middle East, and northern Africa. During their first week of life, the well-hidden baby pigeons are fed a high-fat, high-protein diet of crop milk produced by both parents. They grow very fast. They walk well at about 18 days of age and start exercising their wings about a week later. But because they have been regularly fed by the adults and haven't done much exercising, the birds are often bigger than their parents by the time they start to fly, which is on average 30 to 32 days after hatching. Some young pigeons, or squabs, might venture away from the nest site before fledging, but most stay close to home. So we humans aren't likely to lay eyes on a juvenile pigeon until it is full-grown. maybe even temporarily a little plumper than its parents. and has taken flight and begun to scrabble for food with other city pigeons. http://www.birds.cornell.edu/publications/birdscope/Spring1999/faq_PPW99132.html

Don't know. Pie anyone?

The answer is a little on the unsexy side. Pigeons hide their nests very well, and the babies stay there until they are almost fully grown. Linky: http://www.straightdope.com/classics/a1_015b.html

They don't leave their nest until they're a certain size and once born they grow really quickly.

Probably because they are hidden away on rooftops or have already fallen foul of cats.

Because they do not leave the nest until they have a full set of feathers to fly with, at which point they look the same as adult birds. Most birds grow up very fast. This is because of the nature of flying - an efficient shape at one size is inefficient at another. So birds have to get to adult size (or near) very quickly in order to be able to fly. Birds which fly less, such as hens and ducks, do not need to grow up so fast.

I never thought about it before, but now you come to mention it I never see baby pigeons either. Yet my home city has thousands of pigeons. They must have been baby pigeons some time. Lol:)