Everytime you feed them, even if they are standing at your feet call them.
But a long stick will also help you round them up, stand away from the coop, with the chicks between you and the coop, say "hut, hut!" tap the stick on the ground, the trick is not to stand very close to the chickens. At first you should be far enough away from them that you put no pressure on them. take a step toward them. if they don't move, another step. eventually they will move away from you, toward the coop, check and see what that distance is between you and the chick, keep that distance, the chicks will walk in the direction that you want, but not panicking. Move slow, using your stick to extend your reach to the side, not toward your chicks, your chicks should move slowly to put a comfortable distance to them between you.
Hold your stick out to the side of you for the most part, tapping the ground saying hut hut, you don't want them to run, you just want them to walk toward the gate or door, as you get closer, if one runs to the side. tap the ground on the side you don't want them to go. Don't panic them, if they are running they are panicked. Just move slow and easy, keeping them between you and the gate. If one breaks away, let that one go, and get the majority of the chicks in, most often, the last one won't like being alone, and will be following you in.
The idea is that you place yourself, so that the most comfortable position that the chick can move to, is in the direction that you want. Many people, (perhaps you don't, but some do so I will mention it) want them to hurry to the gate or door, thinking that the faster that they go in, will leave them less time to go somewhere else, but that seldom works.
Mine come running to the coffee can, but sometimes they don't want to go in, and I can round them up when I want doing it this way.
Hope it helps. Mrsk