I had plenty of blue plaid scraps to use up. I cut a million eighty-four 3" squares, sewed them into 12 strips of 7 squares each, and then sewed together the strips. The rest of the steps went by quickly and is like making any pair of kid shorts.
Here is my 3 year old, throwing a temper tantrum because I made him try on the shorts. It really was the end of the world, you know.
And here are a few shots of him a little later, post-tantrum. He eventually warmed up to the shorts :)