Probably originated in a typo (like teh) and was at first popular with scene and emo kids (half of which originated as the geeks who may also speak 1337) but is now popular amongst all stereotypes. Think of the way the skinny jean trend got around (emo kids to scene kids to forever 21 stores across the country) - that's how the kidd trend got around.
To my own experience, it's quite popular in Southern California, but may not be quite as popular in other places (YET).
"Don't call me 'kid.'"
"I didn't, I called you KIDD."