The star paid $20 for his lemonade, which 10-year-old Carter, 6-year-old Chandler and 5-year-old Chase Fontaine were selling for 25 cents.
Clooney made his way over to the lemonade stand Wednesday afternoon after shooting scenes for "Leatherheads," a movie about the early days of professional football that he is directing and acting in.
The boys' mother, Courtney Fontaine, offered Clooney the lemonade for free. He had posed for pictures with her and some other women.
But Clooney insisted on paying, sending someone over with a $20 bill. Chandler enjoyed telling people afterward that Clooney's representative didn't want any change.
Before long, Carter had made another sign that read, "George Clooney was here!" and planted it at the road.
The movie, which is being filmed mostly in North and South Carolina, also stars John Krasinski and Renee Zellweger. It has a December release date.