You can google "rubbermaid worm bin" and get a bunch of ideas and instructions.
I wouldn't use a clear plastic since the worms are sensitive to light.
Also, the smaller the bin, the less room you have form worms to escape adverse conditions and the more chance you will get adverse conditions.

I put around 20-50 worms in the shoe box sized clear plastic container for my daughter's book project on the Diary or Spider and worm. It's small, has to be kept moist and if "inside" should be covered with some kind of towel to lessen the light. Small can be harder to keep due to no place for worms to "hide" from adverse conditions so this is really a short term project.

I think you can use a clear plastic container if you keep it covered completely, like nested in a slightly larger opaque container. Most Rubbermaid bins come in different colors, but identical, nestable shapes and sizes. This way, the worms can remain in the dark 99% of the time, but if you want to show your grandchild the layers, you can pull out the clear tub to check on the worms in not-very-bright light, and then nest them again easily. You'll notice that once you put them into the light, they'll quickly burrow away from it.

Honestly, I'd start with a reasonable-sized Rubbermaid container. I'm guessing that you'll enjoy vermicomposting so much that you'll want to keep on going after April 22nd, and the worms will multiply rapidly within a couple of months, so I'd set it up with room to grow in the first place. The only concern would be not making it too heavy if you're wanting to lift it out of a nesting container to show him. Perhaps wrapping it with a cut-open black plastic garbage bag could keep the light out, make it easy to check on, and negate the necessity of lifting a fully-loaded bin. Just some ideas - take what you like and leave the rest.

Into your container you'll want to put in shredded newspaper or cardboard that has been dampened - soak it in water, but then squeeze it out like a sponge before putting it into the bin. You can bury some defrosted or already-rotting fruit and veggie scraps in the bedding. I'd also throw in a handful of grit or dirt from the yard - this gives the worms some grit for digestion, but also jumpstarts the microbes in the bin to start breaking down that food. If you want to see the worms in action, I'd bury the food next to the bin wall.

Good luck, and let us know how it goes!

Thank you all so much for the advise. I think I will do the clear plastic nested in a bigger colored container so that I can move them later for more room.

We have been cutting newspaper into strips and taking veggie scraps and putting in freezer to have food ready to go for when they get here. No shredder, he needs to practice with scissors lol.

Where should I order my worms? I think we are about ready!

There are many good sources of worms and some not so good ones.
I have gotten worms from these 2 companies over the years and I can recommend them both. Both companies have been around for years and years and both offer a quality product.

http://www.happydranch.com/

http://www.kazarie.com/

I'd encourage you to shop for worms locally - Google can tell you what is available in your area.