I've seen light tables with coloured transparent perspex shapes at a couple of children's museums in the past, and the kids have had a great deal of fun with them, so I thought it would be nice to see if we could have a cheap home version.
I set up the table top I made in this post in the kid's bedroom on top of two old wooden draws that we keep their books in. This made a sort of kid level worktop for them to kneel on the floor and play at. We only had one light that was safe to put on the carpet beneath the table, but that gave plenty of illumination. It was a bit cramped in their bedroom, but that's the only room in the house that I sewed black out curtains for. If we do it with more kids than just the three that I had over today then It may be easier to do it in the garage, that only has two small windows that I can tape some cardboard over. I'll certainly get it out next time we have a sleepover!
We only had a couple of bits of transparent coloured plastic (acrylic stencils), so I had to find some alternative colour sources for the light to shine through. Coloured tissue paper worked really well. I also found the bag of glass nuggets that we'd used way back in the playdough mermaid kingdom. Some coloured plastic popsicle sticks also worked quite well.
I thought about getting some scrapbooking velum stuff, but that was a bit pricey, so I opted for ironing flat a load of coffee filters and letting the kids draw on them with markers and cut the drawings out. These worked surprisingly well.
The fridge magnet letters also let enough light through to be quite cool.
The really big glass nuggets were big enough to draw pictures on, like flowers, fish, planets etc...
It was a nice way to show colour mixing too.
and of course we could use the lightbox to trace things, which my five year old is quite interested in. We've done shadow puppet theatres before, but this seemed to get much more interest over a longer period of time from the kids, because there was so much more to the experience. Having everything down flat made it easier for them to work and being able to draw and colour characters was much more exciting than just having silhouettes, as with a traditional shadow puppet set up.
I don't think you'd even have to go to the effort of making a wooden crate set up like we have, because if you got the right sort of transparent plastic storage tub, then taping white paper to that would acheive just as decent sized area for creating on. I'm sure a lot of people even have them under their beds already!