I love your article, and this is ingenious: Week 3 (Plan B!): I took some chicken wire* and made a 16 sq ft mini run around the brooder, so the chicks had outdoor space that effectively doubled the safe space they had access to. The chicken wire could be elevated using the brooder door and some...
You can make it smaller by duct-taping a board or a towel or cloth across the top to shorten the opening so the older ones can't get in, but they can get out. At two weeks though, I don't think I'd let them get out as if one steps too far away and an older one gets to it, one peck could kill it.
What breed are they and how old are they now?
Could you put a wooden box in the coop with your brooder plate (we used a cozy coop) but then the issue is they need starter/grower feed and water if you can get a small feeder and waterer for them that can fit inside the box so the big ones don't...