Ugh. Sorry. I disagree with the thought behind this. Three strings for "kids as young as six" is just going to give young players another unnecessary learning curve whenever they're "old enough" to move to a six string. Chord shapes they can't learn, tons of songs they can't properly play until they get a six-string. Think about how tough it is for some people to make the jump from a 4 to a 5 or 6 string bass, or how confusing it is for some people to adapt to a 7 string guitar. A lot of players never bother.
For the record, that crappy Harmony I posted in another thread was a gift from my parents when I was 4 years old, and yes, it sucked, and so did I, but I didn't care at all because I was too young to know any better and the joy of playing carried me through. Nothing wrong with a three-stringed instrument as such, but I wouldn't buy one as a "beginner guitar". Start as you mean to go on.