I was 6 or 7 and when we got new carpets at our house, we had a bunch of those carpet sample books lying around. I instantly recognized the opportunity.
My younger brother was commissioned to follow me dragging a huge bag with all the samples. We made rounds in my neighborhood, I knocked on every door, and sold the 4x4 inch samples for $1 a pop.
My USP was "look, you get to choose a sample or two that you like, and the next time you get a new carpet, just show it to the carpet man and he'll know which one to put in". Almost everyone bought one or two samples! For some reason they all laughed because I was being really serious about it all. And I really was - at that age it made perfect sense to me. Then they took out their wallets and gave us a dollar or two.
We nearly got all samples sold within a couple of days, before my dad found out and put an end to our venture. He had to call all the carpet companies we had gotten the nice sample books from and tell them they wouldn't be getting them back anytime soon, since they were now spread around the neighborhood.
He did make new friends with various neighbors who later hit him up about his two ingenious sons, though.
Not a real "job" but my first entrepreneurship, if that counts.