Where were they corning them? It's important with clutter that there's at least an avenue in and out - a piece of clutter pushed up against a wall with no outlet is how they get cornered.
This is a layout of the clutter in my run. Note that I leave spaces around all the objects, so birds can...
Get the area cluttered up, wait a week or two (or until the adults show little to no interest in the chicks) and then pick a time when you can supervise to let them out for an hour or two and see how they interact.