My 9yr old had no trouble "driving" my 10"/F5 at Lostock IISAC. He was even able to use the Argo Navis once I set it up for him. Such a scope is really too big for an 8yr old to manouvre and set up. I may have mentioned to you that I plan to build my son a 6"/F5 truss dob which he will be able to move and use all by himself.
If you're not prepared to build one and are prepared to spend the money this is about as good a scope as you will get for a kid. The 6"/F5 Stargazer Steve truss dob:-
http://stargazer.isys.ca/6inch.html
It aint cheap but its top quality with excellent optics. Also a nice little travel scope for Dad I may add, with 6" of aperture.
CS-John B