My 5 week old chickens wouldn't leave the coop either. I was surprised because they had been outside in the coop from the start and I thought they would be excited to go outside. It took them several days to venture out. Some of them took longer. It was interesting that the 2 week old babies went out the first and second days. I guess it depends on the chicken.
Mine are 6 weeks, and I changed the bedding in their coop. We have 30 + chickens and so i didn't want htem in the coop when i cleaned it. we took the easy going one and put her outside and soon more followed. there were a few I did force out and once they were all the way out they didn't come back in so when i was finished I had to catch all but 5 and put them back in. Now they are all scared of me