Dragons rarely actually hike, but at times the group may need or want to travel somewhere with the whole group, including the little youngsters. Sometimes some are simply too young to fly but more often, they can't be trusted to fly safely and properly without ending up dispersed across the landscape. At these times, you end up with an older adult or guardian who has to carry the troublemakers wherever they need to go.

(Also this proves legs are hard to draw thus explaining why dragons are lazy and love to sleep :3)