Actually, they create a competition in doodle4google. You can go there to discover more.
Doodle 4 Google is a competition where we invite K-12 students to reinvent Google's homepage logo. This year we asked U.S. kids to doodle around the theme "What if...?"
Our winning doodle, selected from over 16,000 entries, was created by Grace Moon, a 6th grader at Canyon Middle School from Castro Valley, California. Grace's lovely doodle, "Up in the Clouds," will grace our homepage, Google.com, on May 22nd, 2008.
16,000 entries - great!
Watch this video to see how Google's Chief Doodler Dennis Hwang draws a Google Doodle from scrap to finish.