Personally, my opinion is that it's a good thing so many kids study taekwondo, just like it's a good thing that so many kids play soccer. The only reason the U.S. has a credible team for the World Cup is because the past 20 years has seen a huge increase in the number of neighborhood kid's soccer leagues. Most of those kids stop playing soccer later in life, but some of those kids keep playing into adulthood...and those adults grow into excellent soccer players precisely because they've been practicing since childhood.
ArchTKD did a fine job of showing why this statement isn't true...
I think we all often hear criticism of martial arts schools that cater to children, but to me this criticism seems misguided, for the same reason that it'd be a misguided criticism about soccer. What are you afraid of, that the U.S. will become a nation where huge fractions of the childhood population have studied martial arts? That some of those students will stick with it and become excellent martial artists later in life?
I don't actually hear this criticism much at all. What I do hear criticized (and agree with) is the practice of giving out baby black belts. Just as your average neighborhood soccer player doesn't deserve a shot at a professional team, neither do they deserve a black belt. Our school has lots of kids. They have a great time. They learn what they're capable of. They do extremely well when they compete against students from other schools, and frequently do so against students of nominally higher rank.
But you won't see them wearing black belts.
I mean, what's the alternative? Imagine we didn't have the "McDojos" (as some people call them). What would that be like? There would be fewer martial arts schools in the U.S. Fewer adults who trained since childhood. Fewer adults who become truly outstanding martial artists. Plus, the fact that every strip mall has a martial arts school just makes it that much easier for adults (like me) to finally discover martial arts. Is that really so bad?
I think it's fantastic that the U.S. is developing a tradition of teaching taekwondo to huge fractions of our childhood population. There's no downside. There's only upside.
A McDojo is not a school that caters to children. A McDojo is a belt factory. "If you can afford it, we will award it." is a reasonable description.