Adult bluebirds always stay busy trying to keep nestlings fed. You can tell the nestlings are nearing the fledging point when the adult bluebirds feed them from outside the nest box in order to entice them to peer out of the entrance hole at the world. The importance of feeding meal worms during this period cannot be overemphasized. If possible, place a mealworm feeder in the vicinity of the nest box and keep it well stocked throughout the day.
The YouTube movie clip provided below shows the adult bluebirds shuttling between the mealworm feeder and the nest box to keep the nestlings fed.