HELP! Bird's Nest In Bathroom Exhaust Vent

I don't know what kind of bird it is. I heard some noise in the vent about a week or two ago. I flipped on the fan and pounded on the ceiling around the vent. I think I heard the bird try to stop the fan and I heard a squawk. I've been turning on the fan every morning when I've heard some noise in the vent. This morning I heard baby birds chirping. I don't really want to harm the bird or its babies. Will the mother bird continue to use my vent in the future? If the eggs have already hatched, how long will it be before they leave the nest? I want to clean out the nest after the babies leave. How did the mother bird discover the vent in the first place? It's flush up against the side of the house half way up the wall, there is a flap covering the vent. There is nothing for the bird to land on, how did it gain access to the vent? On windy days, I can hear the flap flapping in the wind. Is there some kind of mesh insert/cover I can buy at the hardware store to prevent this from happening again in the future?