Sell it during a yardsale. Wanna know why? People will see you selling junk which people like to do anyways, but then they'll see the little girl with the lemonade and think it's adorable, so they'll stop for the lemonade and then they'll feel bad about not buying from the yard sale or vice versa. Also it's more likely that old people come to a yard sale, and as we all know, old people can't resist cute little girls.
Also be sure to sell brownies with the lemonade. Say you'll sell a brownie square and a lemonade for 75 cents. It works everytime!
Good luck! ;)
With all regards,
-ChrisTom