If you want them to sleep on the roost/ in the coop, in my experience, at a young age, if you go out just after dark and physically relocate them to where you want them, they learn pretty quickly. ALSO in my experience, if you don't they may not, ever. I have one group that refuses to sleep in the enclosed coop and sleeps in the open in the (enclosed, secure) run. So it's worth doing. You'll need to commit to going out to relocate several nights, up to a week. If you have a headlamp with a red light it will help (they can be found easily at Lowes).
They are about 2 1/2 months.. there is six of them.. our main concern is we have woods behind us and it is not unusual to see a coyote, deer or raccoons.. we recently just had a snapping turtle attack one of our ducks, posted in another thread..
when we built the coop we did dig down about 3-5 inches and added the wires and filled with rocks for extra security in case anything did try to dig into the coop.. it's currently their second night in the coop and we do go outside and have to place them inside the coop one by one, of course they want to stay outside.
That's young. I would physically relocate them all to where you want them to sleep once it's dark enough for them to stay where you put them (about an hour after sunset or so). Do it every night. They will learn (some faster than others).