in Japan they teach the kids Judo from early on, as a form of physical fitness and a basic introduction to martial arts... the philosiphy(sp) of martial arts is just as important as the physical aspect... respect, honor, etc... i believe Judo is a good introduction to martial arts, learning how to fall, roll, basic punches, kicks and throws... you can't go wrong with Judo for kids, but i started Kaju in the 4th grade(about 9yrs old w/GGM Iverson), after a few "summer fun" park dept. Judo classes and what i learned in the first few weeks of Kaju covered all the basics of Judo... its easy enough to take what you learned in Judo and apply it to Kaju so Juda is a good option for youngsters, but i think if they are gonna(eventually) study Kaju then they should probably start out with Kaju, instead of starting out with TKD and switching over to Kaju... when i moved away from my Kaju lessons i signed up for some standard "McDojo" Karate(ka-ra-tae) as the haole's say it... as a purple belt(2nd belt aft white, under GGM Iverson) i was much more advanced than alot of their 3rd and 4th level belts... what they taught me in Kaju was way beyond what they were teaching to their young students... as a black belt you probably have some experience as an instructor so for you to hold some classes in your garage wouldn't be such a huge feat for you as an instructor(Sifu)... this is also an opportunity for family time, you can teach your wife some basic self-defense too... maybe the kids friends in the neighborhood may be interested also, maybe some parents too, you could turn it into a neighborhood watch/seld defense class... just think you should avoid the TKD classes esp if the long term plan is Kaju...