We keep all the food, water, roosts, and nestboxes in our coops. Our chickens apparently think of it as "home" and they go in automatically when it starts getting dark, all I have to do is go out there and close the doors. (We have racoon problems at night, so they get locked in from sunset to sunrise.)
ON MY WORD! I cannot believe how simply this all worked this evening! Thank you everyone for your replies! I put the food and water back in the coop and let the chicks get used to it being in there today. They did very well going in and out all day. Then, at dusk tonight, I went out and saw they were all huddled in the same corner again, so I turned on the light in their coop and within MINUTES they were walking up the plank, one by one until they were all in there! I went in and shut the coop door! Simple as that!