I'm no Picasso.
(Because Cubism, get it?)
But for this craft, that really doesn't matter. I mean, sure, Cubism was the first abstract style of modern art and it was developed by the actual Picasso (and Georges Braque, but no one ever jokes about not being a Braque). And yeah, the actual paintings are quite complex.
But the goal of crafts for lazy parents is to get kids learning and crafting with a minimum of parental work, not to turn kids into world famous artists. Or even art history professors.
Here's the part where I suggest books. Do you have to read the books first? No, but it helps if the kids have heard/read them at some point. Do you have to buy the books from the links I provide? No, of course not, what kind of fascist do you think I am?
Now, for the craft. First, have your kid draw two large faces:
(I believe we've already covered the fact that I'm not an artist. Ahem.Also, the project looks cooler if the faces are colored in, but I was in a hurry.)
Encourage him/her to add details like eyebrows and nose rings. Crayons, markers and colored pencils all work for this; choose the one that your kiddo likes best to maximize drawing time. But don't let your darling get too attached to the portraits, because next your going to cut them into squares.
The size of the squares is up to you and/or your child's patience. The older the kid, the smaller the squares can be. These are going to be the "cubes" that your kiddo "paints" with for the final step. The final picture is a mash up of both portraits:
I would let kids move the different squares around and try out new arrangements before handing over the glue stick. Depending on your kid's enthusiasm level, you can let him/her make up to three different collages from the two portraits.
In actual Cubism, the artists also looked for other shapes found in nature, so you could extend this project by have them mash up two house drawings by cutting them into rectangles, or mash up to trees by cutting them into triangles.