I don't know much about the lego mindstorm or anything but our team does have a FIRST Lego League Team.
I would reccomend
FIRST Lego League if they have it avaible in your area. FIRST Lego League is mainly for 9-14 year olds but I know our FIRST Lego League team has students even younger than that, so you'd probably want to contact your school system or the schools in your area.
Another product out there you might want to look into is VEX which you could buy at Radio Shack.