Hmmm...knives for kids...somewhere around fivish, depends on the kiddo...the exMrs.Guttery still won't let my first daughter have one, and she's six...but she gets to use one over here (under supervision).
 
_________________________
Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space,  a critter that can be killed but can't be tamed. --Robert A. Heinlein