We are on the extreme western edge of the Chimney Swift populations in the U.S. Before chimneys they nested in holes in trees, after migrating from the upper Amazon River. To get pictures of the babies isn’t that difficult. Simply get an extension cord with a work light on the end of it, climb onto your roof, dangle the light down the chimney until you see the babies, then snap your shot. Your neighbors may think you crazy, but they probably think that already. 
Yes, they cling to the side of the chimney. The nest is made of twigs and saliva, which the young eventually eat. The birds winter in South America.
