I've been the co-ordinator of the science fair program at our elementary school and my older children have competed at the state science fair in Texas. I've posted a hub (How to make a great science fair board and experiment) which gives links to science fair activities as well as a number of Hubs which give step by step photo instructions for science activities like seeing which chewing gum is best? which chocolate melts first? which boat shape floats better? How salt affects seed germination?
I'm in the process of posting more instructions. I also have a hub on Crazy kitchen science experiments like exploding marshmallows in the microwave and making slime, and how to test for acids and bases in the kitchen. I'd tell more here but the Hubs give pictures and full instructions--just go to my profile page.