They are made out of a 'baby cord' cotton fabric printed with a mechanic's equipment - wrench, gas pump, tires, etc. Perfect for a young lad. Found in my stash from my days working at Fabricland in Uni when I made things (but not these obviously) for my then young cousins (who are now in Uni themselves).
This is what they looked like moments after coming off the sewing machine. Notice they are a bit brighter! They have been worn often, become softer and well, a bit lighter in colour.
Here is a close up of the front - and you can see his personalized label in the back of the waistband too. He really likes the front pockets. Big enough for Hot Wheels cars!
And the back with its cute patch pockets.
Oliver + S Pattern - Sandbox Pants (digital pattern)