Re: Is aikido suitable for children.
I realize that there are some very competent aikido instructors out there who are doing good things with children. All the same, I do not think aikido is appropriate for young children, for at least two reasons. First, aikido techniques, even applied gently, put stress on the joints. As many former gymnasts and ballet dancers can tell you, too much stress on the joints at an early age often leads to trouble later on in life. Second, aikido is a complex art. Even disciplined, motivated adults find it quite challenging to learn. In my experience, younger children do not yet have the ability or the motivation to concentrate at the level necessary to gain anything from the average one-hour aikido class.
But more important than the physical impact or the mental challenges, there is the ethical question of teaching martial arts to children. Study of the martial arts, like the study of any other art or discipline, can produce wonderful effects on the student's character. But I believe that teaching young children martial arts is like teaching them to drive: it puts them in possession of power before they are mature enough to use it responsibly. Some teachers will say that they teach the ethical use of martial techniques, but I would not want to depend on the developing moral compass of a child outside the dojo; it's just way too likely that the child will want to try out this new-found knowledge on the other kids!
Rather than martial arts, I recommend introducing children to disciplined physical activity through more conventional sports and arts (such as soccer or tumbling), in which there is a far more well-established tradition of teaching children. If the child continued to show interest in the martial arts, I would hold that out as a future reward for good behavior and a helpful attitude around the house and with other children and adults --- in short, the child would earn the right to train in the arts. It seems to me that is closer to the spirit of Japanese martial traditions: if someone wanted to study at a dojo, it was necessary to present a letter of introduction to the instructor which vouched for the prospective student's dedication and good character. Unfortunately, this tradition never caught on in the USA.
In my own dojo, I set a minimum age of 14, which is just slightly below the age requirement for driver education. The teen and at least one parent must watch class before the teen may join the dojo, and at least one parent must watch the teen's first class. I encourage parents to visit the dojo at any time. The teens practice with the adults, and I and the other yudansha keep a close eye on these interactions.
After 5 1/2 years, my dojo is relatively new. About a dozen teens have come through the doors, and I have noticed that almost all of them have schedules that are far more demanding than I had 30 or so years ago. Very few of them have the time or the will to commit to pursuing proficiency in anything, let alone aikido. I've always looked at aikido as "graduate-level" martial arts practice, though (I know, I know --- that's another thread), so it does not surprise me that junior high school kids are not up to the task.