Cheap, easy and quick; making your own kaleidoscope is a great activity to do with the kids. It took us about 20 minutes to gather the materials together and make 2 kaleidoscopes and the kids were very impressed with them.
We found the idea here and made our own like this:
1. Find a cardboard tube and some shiny reflective cardboard which is about 5-7mm shorter than the tube (if you have big beads you might want it to be a bit shorter, small beads = longer).
Note: we used toilet paper rolls which were just a fraction too short for our adults eyes to see the beads in focus giving it a lovely blurry colour effect. Although I don't think the kids had the same issues.
2. Fold the cardboard so that it makes a triangle which fits snugly into the tube. Shiny side goes in.
3. Find some fairly stiff clear plastic (an old bit of toy packaging worked perfectly) and cut a circle the same size as the tube.
4. Fit the plastic circle into the tube up against the triangle. There should now be a little room at the end of the tube to fill with beads.
5. Fill with beads of your choice (or any small shiny things you have). See through things are very effective. Leave a bit of room for the beads to tumble around when you turn the tube.
6. Use a piece of white tissue paper to cover the end up, so that the beads are safely in between the plastic layer and the tissue paper layer. You want the tissue paper to be thin enough for light to shine through.
7. Stop and check that you like what you're making.
8. Cut a piece of heavy paper to go over the other end. Cut a small hole in the middle. Press the cardboard gently against the tube so an imprint of the tube size shows up.
9. Cut lines into the tube imprint circle.
10. Sticky tape down every second tab.
11. Sticky tape down the rest.
12. Decorate with your choice of pretty paper.
13. Use a small piece of clear contact plastic to make the tissue paper strong enough to stop small fingers from accidentally making a hole in it.