I'd like to bear my testimony of the importance of buying whatever kids are selling.
Even if it's potentially contaminated lemonade that you have to discreetly dump as you turn the corner. Or cookies that may or may not have been made by someone using proper sanitation practices. If kids are sitting out on a corner stand waving their signs - BUY IT. And we'll all make the world a better place.
(though honestly... someday when my kids are old enough to be the ones sitting out there selling junk... I'm not going to do all the prep work, like I'm sure these kids' mom did. Those cute signs definitely weren't made by a 7 yr old. Where's the lesson on advertising and marketing fees?! And the 25 cent cookies looked totally mom-made. She better have submitted her hours for that, and possibly filled out a W-9. And I bet these kids weren't taught about overhead costs, like paper cups and ice cubes. I'm such a party pooper, I know. But my kids are going to be excellent business people someday after learning the tough lessons as young lemonade-peddlers!)