In our renmei, the children are very important. We have over 50 junior members, most between the ages of 5 and 10. It was explained to me when I joined that martial arts practice in general is on the decline in Japan, i.e. the younger generation (teens - 20`s) are not that interested in them. In order to protect the future, it was important to start when they are young. All of our dojo`s have kids classes, and there is no shortage of sempai helping them out, often, there will be at least one sempai per 2 kids.
Of course the technical and spiritual techniques of the children are not going to be the same as adults, not at the start, but maybe in 5 or 10 years time they will be. Having said that, I am constantly amazed at the abilities of some of the little ones, and it is fantastic to see 4 year olds doing over arm ukemi from kotegaeshi (much softer of course) with Sensei during embutaikai`s.
At the All Japan embu a couple of weeks back, there was a great embu, where a little one who couldn`t have been more than 2 or 3 years old, was tori doing kokyunage`s to (presumably) dad as uke.
Personally, I agree with the renmei thinking, the kids are important for the future. My dojo back home in the UK doesn`t have a kids class, but I hope that when I return, it will be something that I can help with.