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This is a common "issue" encountered by new chicken keepers when they move their chicks from the brooder to the coop. Chicks being raised by a hen would have just naturally learned the routine by following along behind her - in the case of brooder raised chicks this is not possible so you become the hen and teach them the routine. There are a few ways you can accomplish this, which is best will depend in large part on your coop and what method can be used in it.
Is your coop one with our without much in the way of windows? Is your coop large enough to accommodate you going inside or is it one of the smaller types?
From the chicks' perspective, they stay outside as long as possible - until the last bit of daylight is fading. Unfortunately, most coops are such that by this time the interior of the coop is pretty much pitch black dark and looks more like a scary, dark cave than in inviting haven of safety -- so, instead of going inside they end up huddled up outside in the run. Mature birds go in before the last minute, fill their crops, get a few drinks of water and get to roost before it is completely dark inside the coop.
As dusk starts to settle, go out and start your training of the chicks so they learn that the dimming of daylight is the cue to start your bedtime routine. One easy thing that can help is to use a small light (can be a battery operated flashlight/lantern if no electric is available) so that the interior of the coop remains lighter than the outside - making the coop more inviting than outside....as it gets darker outside they are drawn into the light.
Have you taught the birds to respond to being called or respond to the noise of a favorite treat? From inside the coop (easiest if man sized, possible in smaller coops with a little imagination) call to them and rattle that favorite snack so they are drawn to come up into the coop.
Alternatively, you can gently "herd" them up the ramp and into the coop or, if need be, catch them and place them into the coop -- the last one is my least favored approach because I prefer methods that have the birds making the move under their own power vs. having it done for them.
For the first few nights it may be helpful to go ahead and block the door so that they have to stay in once you get them in. This will help them learn to go to roost and settle in vs. trying to run back out and ending up "stuck" outside again.