They're bonny birds. What a shame Chris. :( Tomorrow, get any birds that you have already trained to home, out and flying in the hope they bring your YBs in.
You've got a sputnik right? What I do is put the babies in the sputnik well before they can fly, even before they are weaned - they get a good look around for a few days. Then, again before they are flying, I put one at a time out on the landing board. They hate being out on their own and soon find how to drop back into the sputnik. After they have done this three times I reckon they know how to trap so I put them all out together on the landing board but close the sputnik so that they can't get back in. Remember, these birds are still not flying. The birds explore the sputnik and, as they get more able and braver they hop up onto the loft roof and, over the next few days begin to take little flights around the loft. All this takes time and I don't leave the birds alone because they are vulnerable to predators. At the same time I am also training them to the feed can...I open the sputnik and rattle the tin to bring them in.
This is only my way of doing it - there seems to be lots of ways and you have to find one that suits you.
Young birds learning where they live.