The young are getting close to leaving the nest. They’ve been getting up to the nestbox entrance hole and looking outside. At this point they will leave any day now and as they normally leave the nestbox as soon as there’s enough daylight for them to see I’ve got my alarm clock set to be at the nestbox half an hour before sunrise.
They’re also exercising their wings in preparation for flying the nest. This doesn’t go down well with their brothers and sisters at times.