Citizen science is a fun way to participate in a bigger science project than what one can do at home or even in a lab. Citizen scientists help collect data for professional scientists to analyze--think bird counting or amateur astronomy. Or they can help analyze and report on data that has been gathered by professional researchers.
At zooniverse.org, you can mark and measure craters on images of the moon, help model the Earth's climate 100 years ago by transcribing Royal Navy ships' logs from World War I, or identify species and ground cover on the sea floor. These are just a few of the science projects available to work on and there are over 800,000 people taking part worldwide. My son and I analyzed some photos of animals in the Serengeti that were taken with motion-sensor-equipped cameras.
Scientific American has a list of current citizen science projects.
Scistarter.org is a kid-friendly portal for citizen science. It helps budding scientists find projects based on topics, activities, locations, cost, and more. Some of the projects are gamified to add more elements of fun.
Please let me know in the comments if you've participated in any citizen science projects, or would like to.