The boys first garage sale

So it started out that they wanted 30 dollars to buy some star wars figurines but because their birthday is so far away and bad mommy has not set up their bank accounts they have no money nor pocket money nor did they want to do housework... So they decided to sell some of their toys in a quick garage sale. Here is a picture of them... Am tempted to pay a kid to go buy something from them! Now how do we teach them advertising and pricing?