they can count as one person
on shoulders
(glued eel/questions/questionsyoudliketoask/post1648081, Sun 5 Apr 2009, 22:10,
archived)
legally just the driver.
technically, and of course I have never ever done this, it is quite possible to have a child sitting on your lap, standing on the footboard, or holding on to the back of the seat while standing on their rollerskates.
(Batsgirl, Sun 5 Apr 2009, 22:12,
archived)