We put the big brooder in the shed brooder yesterday, and put a pre-warmed brick inside for Number 6 to stand on. We put a pre-warmed brick outside for the others to look in.
For ages, the chicks didn't notice this...thing.. inside their newly enlarged area. Eventually a couple of them got on the brick couldn't see anything, and jumped off again. Number 6 jumped on his brick each time, but by the time he got there, the visitor had gone.
DH opened the corner of the door so it was easier for them to see in and out.
All was well.