Ohhhh, they're young AND they're Silkies. They're a breed not known for being the sharpest tools in the shed (I have them and I love them, but its true). You'll probably just have to pop them in the coop until they get the hint. That's what I had to do with mine when I had a coop with a ramp.
Heck, my current coop has a 6" lip at them bottom of the door, and I still have to pick up new additions and put them in for anywhere from a couple of days to a couple of weeks!
Good luck