Carlos trackman IMHO is a great tool but for young children building on the foundation of their swing fundamentals and enjoyment of the game might be a more important priority at the moment. 

I would find an instructor that you are comfortable with (maybe one that has access to trackman) and allow the instructor to determine "when" is appropriate vs. anything else...one instructor in our area only begins using trackman for high school and college players not at earlier ages...

I have used trackman for years and it has lots of great data however it may be too much for young kids...

Good Luck!

To me, that sounds like too much too soon.  In my opinion, at that age you want to focus on good habits and course management.  Golf should be fun for them.  They should spend more time playing "games" than working with a trackman.

Thanks for your reply i have the same opinion .

THANKS FOR YOUR REPLY, I ALSO THINK THAT FOR THE KIDS WILL BE VERY CONFUSING TO UNDERSTAND THAT KIND OF INFO.

I just had my first TrackMan session last week.  I was so impressed with the information that I picked up on with my swing and the results that I'm planning on a monthly session.  But honestly, I can't imagine an 8 or 9 year old being able to get anything from all of the numbers and diagrams that that thing spits out.  Now, the session I had also included video of my swing which I don't know if that is always part of a TrackMan session or not, that might be somewhat helpful for the coach in showing where improvements could be made?  Maybe the coach will be using the TrackMan info just for himself to use as a training aid?