Things to Make - Science Experiment Kits for Grade Schoolers
Over winter break, F's teacher sent home these "science kits" with each of her students. The kits include directions for 10 relatively simple experiments with succinct, understandable explanations (when people teach science to kids, I find that they often go for the "bang" over the explanatory, thus my children rarely understand the difference between magic and science). Nothing too messy. Nothing too complicated. Plus, Ms. C included all the necessary materials (toothpicks, marshmallows, etc.).
By the end of break, Dan had the flu and my foot remained broken, so our days weren't exactly fun-filled. Luckily, this kit kept T and F occupied for an entire afternoon. And they worked together (with F reading the directions and T putting the pieces together) which is a miracle in itself. A winter break miracle.
When I wrote Ms. C to thank her, she told me that the instructions for the kits (there are several) are available for download from this website. I think these would be awesome for birthday parties, either as favors or for the party itself. Or even just store the kits in the closet and have them ready for a rainy/snowy day.