It is good that they like their new home. They should go in there to roost at night with no problems. So you are in good shape in that respect.
Chickens are not trusting creatures. They have the instincts of prey animals, not predators. They usually do not like anything new. If they are not used to it, that open space out there is big, frightening, and intimidating. But given time, one will work its courage up and explore. The others will soon join the first. I agree. Just leave the gate open and let them decide when to go out. There is nothing wrong with scasttering a few treat just outide the gate to help them get brave, but there is no real reason to rush it.
One thing I've learned is that chickens do not handle the concept of "gate" very well. They quickly learn to use the gate, but they do not have the ability to reason out that "There is a gate over there. If I go to the gate, I can get to the other side of the fence."
Usually the first one or two days I let a group of chicks out to free range, some get on the wrong side of the run away from the gate and cannot figure out how to get back in. They are up against the fence, desperately wanting to go to the coop and safety for the night, but they just can't get through. This is usually two or three out of maybe 15 to 20 chicks. I herd them around the run to the gate and they go in. Most usually catch on the first time I do that, but last year I had Buff Orp pullet that had to be helped two nights in a row. The second night I herded her in, as she went through the gate she looked back over her shoulder at me as if to say "What took you so long?"
