When I checked the box on 6th June this is what I found:
As you can see, the chicks have grown and are big enough to be ringed. Note also a dead chick in the top of the photo. This bird is also a juvenile bird, but not one from this brood. My only idea is that this bird came into the box to roost, and was possibly killed by the adult birds? The dead bird is obviously a health risk to the chicks, so I removed it when I ringed the chicks.
I contacted my trainer, and got hold of the "C" rings that a Starling takes and ringed the chicks today.
I think the chicks will be in the nest for about another week, after which I hope they will fledge successfully, and then start feeding in the garden... and beyond!