Iain, i'd suggest starting them off with some simple kicking relays where they get used to kicking a ball thats not round, use the grubber kick where they follow and pick their own kick, then some more difficult practices where they control the ball by kicking it back into their own hands while running. For a warm up i'd suggest crazy football, its football but played with a rugby ball instead and good fun, progress by adding more than one ball to the game. once they can control the ball and kick accurately, then progress to more difficult techniques kicking the ball to each other using spiral, punt and end over end kicks. Keep attention to detail, practice off both feet and accuracy is the key.