Thanks for the suggestions :)
This afternoon i placed each chicken near the bottom of the ladder and they all walked up fine. Left them for a while and came back to one of the chickens sitting half way down the ladder. Woohoo! We have made progress.
As the title states my chickens won't go up or down their ladder. I've tried putting their food at the bottom to try encourage them but they won't budge. We have placed them on the ladder and they can definitely climb it. Any suggestions would be helpful.