a “smoking apparatus” - usually a glass bulb with two or three necks - the cigarette gets “smoked” through one, and the smoke gets pulled through a filter or condenser and/or sodium hydroxide trap via a vacuum pump. This demonstrates the extreme nastiness that gets pulled into your lungs when you smoke - seeing the tar on the glass and smelling the resultant goo makes quite an impression.
Agar plates, sterile sampling swabs and an incubator with a viewer for counting resulting colonies - kids can test the bacteria on toilet seats, doorknobs, the floor and even their mouths - and be disgusted to find the results! Awesome! (Just saw that they will only be there for an hour - you can do the smpling/growing, and show them the results. Not quite the same, but still great ICK factor.)
a geiger counter - a cool toy kids will love, plus you can count the radioactivity of some everyday objects - helps demonstrate that radioactivity is something we are surrounded by and part of the natural world, not something to be feared
I had a science lab for kids for the previous 13 years before I moved to an educational non-profit. I had lots of the equipment folks have mentioned but lots more that kids actually loved. Children thrive on being able to use things in novel ways and autoclaves, centrifuges, flasks and test tubes don’t lend themselves to much creative use, at least for elementary/primary school children. Science is creative, but I think the way it’s presented to kids emphasizes a completely non-creative kind of science. A rigid scientific method, careful use of precise tools, pre-determined outcomes; why on earth would I want to do any of that at age 10? Let me explore!
Anyway, my students greatly enjoyed using triple beam balances, and hand tools (drills, hammers, saws) K’Nex, alcohol burners, stream tables, tons of electrical stuff—1.5v motors, 1.5v lights, etc.—Magic Sand, household appliances…
If you’re interested, email me privately and I’ll send you the last inventory I made before I left.
Contact you local hospital laboratory and speak with some of the techs or supervisors there about them letting you take some of their expired tests, reagents, stains, whatever. Glucometer test strips, urine dipsticks, and ABO/Rh anti-sera all work rather well past expiration date. They are all rather easy to do and fun lab tests that can possibly spak interests in the kids to work in a lab. I know I have a blast as a lab rat.
I mean, you could throw lots of money at the project and buy flashy equipment like HPLCs and confocal microscopes, but without the basic knowledge of what these machines (or others) do and why they’re cool, you may as well just have screens with powerpoint presentations on.
Most big science museums have specially designed areas for kids (and adults) (such as the Science Museum’s Launchpad) to play and experiment with various concepts, but the experiments are designed in such a way as to not only demonstrate the concept but to give a context and its real world application.