If you or your kid want to learn to play guitar left-handed, but don't want to fork over a lot of money to buy a special left-handed guitar until you know if you are serious, here's a suggestion. You can modify a cheap, used right-handed guitar by doing three things:

(1) buy an old guitar with a floating bridge (the part that holds the strings up off the top of the guitar); if the bridge is glued to the soundboard (as most are) this will not work! Take the strings off and reposition the bridge 180 degrees, so that the grooves for the fattest strings are at the top. (If the small bridge at the top of the fretboard is floating, invert this as well).

(2) The holes in the pegs may or may not be a problem. If you cannot fit the fattest bass string through the appropriate peg hole, make the hole larger, using a round file or metal drill.

(3) Before you made permanent modifications to some old guitar with a floating bridge that you've found at a yard sale or pawn shop, make sure it isn't valuable! (e.g. like an old Gibson).

From M.K.Holder, music tips:
http://www.indiana.edu/~primate/lspeak4.html#guitar1