In the past we have had a wide range of bikes make it through the course just fine. Although a dual sport bike would be acceptable for the skills covered, a "smaller" bike would be of increased benefit for your learning; that is a bike that is lighter and more maneuverable.
Also, there is a lot of clutch work involved in most of the fundamental exercises we do on the first day, and it revolves around having a clutch to adequately conquer the skill. If the bike does not have a fully functioning clutch, like a 50cc for a child, then probably the child should wait until they are ready and comfortable on a bike with a full clutch capability.