Inventions - where to begin

My oldest child has an almost unnatural affection for firearms, as does my third child. So we may begin with the history of guns. I did find some very interesting info on them:

Science and civilisation in china

Great info overview here of "Handgonnes"

The firearm blog had this little tidbit of history here.

Of course I have a mild obsession with Da Vinci, so I'd rather study his numerous inventions, so I'm gonna have to find a happy medium.

Actually I think he has a drawing of a mechanism that was later incorporated into guns. Let me see if I can find that one.