Honestly chickens are terrified of everything and take a while to get used to stuff lol. No wonder we tell people who are scared to stop being such a chicken! When I first brought mine outside, I had a carboard box that had no top or bottom and I covered half of it with a towel. It seemed to be ok for mine. When I put them out in the run for the first time they were out there full time and just had to cope haha. I would suggest maybe giving them somewhere to hide? like maybe even if you have a box, just flip it over and cut out an opening for them to go into. Or something for them to hide under. Then with a bit of time, they will start coming out. You could also bait them with treats