The first ever attempt to measure the acceleration due to gravity in a public park using volunteers all under 10 years old. We presented the results the next day, complete with error bars, at our family event "Experiments That Changed The World" at the Cheltenham Science Festival - it was surprisingly close to the expected answer!
We also re-created the Eureka! moment with fake gold crowns on stage, and even got a mention in `The Times' which I helped to write
"Want to have your Eureka moment? Help a team of top scientists to recreate three classic experiments in a special event for families ... at the Cheltenham Science Festival" (The Times)
The hammer and the feather - not on the moon - a classic. Thanks Meeks.