I would check out the science olympiad elementary level website (for K-6) for ideas. Even if you have no intention of joining/starting a team, they have tons of great ideas. We don't have elementary level SO here, but the middle school stuff is fantastic- the kids delve very deeply into their events (here they use college level and AP texts, tons of online resources and local mentors when they can find them). The events are great jumping off points, and the science olympiad home website and forums have tons of great resources.
www.soinc.org Look for links to elementary SO and sample K-6 events. The forums are used by middle and high schoolers, no elementary schoolers as far as I know, but you might find ideas there, too- (probably more than you want for age 6 but you never know).
www.scioly.org
