Helpful Links and Documents:
Science Buddies: http://www.sciencebuddies.org.
This Web site is designed primarily for science fair projects, but these activities also make great projects for 4-H science displays or science learning activities that relate to 4-H projects. Projects are by grade-levels so they're age-appropriate. There are discussions about topics like scientific method, doing research and constructing a hypothesis. It also has an "Ask an Expert" feature.