It is interesting that some people do tkd as a shared hobby with their kid/s. It some sort of common bond they can have both inside the dojang and even at home practicing form together in the lounge room. For others it's a release, its that time they get away from the wife and kids and work and mowing the lawn etc etc, and the last thing they would ever want is to share it with someone else.
I think it's about having enough options that something will work out for everyone. And, that's going to be different for different people in different places at different times in their lives. I began Taekwondo before I became a mother. The class I started in happened to be a family class just because that's what worked for my work schedule, not because I had any particular thought about it one way or the other. Then an injury, graduate school, and then mothering contributed to keeping me from practicing for a few years. My next opportunity to practice Taekwondo was also a family class--with my then six-year-old daughter. She and I were still practicing four years later when I adopted my youngest four years ago. With my baby strapped on in an Asian-style baby carrier, I would help teach class and gently practice poomsae or whatever else could be done without risk of falling. Now I teach a family class. My youngest practices Taekwondo with me and my oldest daughter (2nd poom waiting to convert to 2nd dan) is my assistant instructor. Without the option of family classes, I never would have been able to continue in Taekwondo. Most of the students I teach now would not be practicing Taekwondo without a family class, either. But, some come just because they like the intergenerational atmosphere as a refreshing option in a highly age-segregated culture.
Cynthia