You can tell when an adult is coming because the young flap their wings and make high pitch twittering.
Occasionally the adults come and knock the young off when feeding, I don't know whether this is by accident or on purpose to get them to have a go at flying.
If the young do fall off they fly around for about five minutes, then lands again.
Once the fledglings are in the air the adults have a go at feeding them on the wing.
The next three photos are a sequence showing the adult feeding the young without stopping.