I had the same problem with my very first batch; what I ended up doing is giving them a yummy treat in the coop at night. I don't recommend this as a continuous way to raise them, because I want mine to associate the coop with sleeping and laying eggs; they should go outdoors to eat and drink (except winter). But, in this instance, it really did help.
I began by using an old stainless steel dog dish. I ran it through the dishwasher to get it nice & clean first, then mixed up yogurt and oatmeal, and just set it out in the run. Then the next night, I moved it right outside the pophole door. After that, all I had to was ENTER THE RUN with the stainless steel dish and they'd run to the coop - I'd put it on the floor, they'd gobble it up, and while doing so, I would close the pophole door and make sure they were secure, then turn out the light last night when they were done. They really do associate the dish with a treat!