I haven't toured (yet!) with my kids but I've taken them backpacking, canoe camping, etc. That said, I think 9 is a bit young for a child to be on his/her own bike sharing the road with cars and trucks. Best bet at that age would be a tandem, IMO. It all depends on your kid of course but 1 misstep could be fatal.

Otherwise, start small and keep it fun. It's much better for a trip to be short - but fun - than to have the first time out be miserable.