Wolfie and Xavier got a bunch of "Harry Potter" science kits for Christmas at American Science and Surplus. http://www.sciplus.com search for Harry Potter
For less than $2, you get 3-5 experiments on a theme ("alchemy" is chemistry, "Herbology" is botany) with some supplies all in a plastic/tyvek bag. We have "homework hour" for my public-schooled boys every night after dinner--if they don't have homework they do their Harry Potter experiments and just love them. The experiments are short (<30 minutes) and very well-explained in the instructions. One had the classic Cartesian diver experiment, which I've done at least a dozen times in class and teacher-training--the HP kit was the only one which explained how it worked in a way I understood! As you can tell, I can't say enough good things about these kits.