I think we've known for a really long time that all children become less active as they get older. We also saw a plummet in positive psychosocial health indicators as children approach adolescence. So there's no difference, really, and we have known that for a long time. Those figures are just being exaggerated now in terms of physical inactivity.
I don't think that girls are any less active. The problem is no less of a problem in girls than it is in boys, in our data anyway, in terms of why children are generally becoming less active.