Ok, this is a common problem with chickens that may not be raised by a mother hen or have older hens in the coop. Basically, they don't have a "role model", so you're going to have to play parent and teach them. No, you do not have to jump on a roost bar, but you'll need to place the birds on the roost bar at night. Essentially, when it is dusky, you'll go out and put them on the roost bar when they go into the coop. If they protest, wait until it is completely dark. Even the most rowdy birds remain motionless at night because chickens have horrible eyesight. Place them on the roost bar at night. They will eventually get the idea. Might take a few days, but they'll get it. Also, make sure your roost bars aren't set too high. They should be able to hop up there pretty easily. The bars can be raised when the hens get older.