On the other hand, I was talking to one of my friends about this who spent years living with forest tribes in the Amazon. Out there, kids use machetes as part of everyday life from the moment they can lift them. You'd think 'ah, well they learn to respect them as tools not toys', but my mate said he had seen some of the most horrific injuries occur, even deaths. Kids are kids even when they learn it from the cradle.
Incidentally the same thing applies to fire - he'd seen kids terribly burnt, usually on their backs from falling backwards into open fires.
Sorry Lannyman, don't want to scare you, I guess the answer is 'watch 'em' like a hawk!