Check out Qimo.
Qimo is a desktop operating system designed for kids. Based on the open source Ubuntu Linux desktop, Qimo comes pre-installed with educational games for children aged 3 and up.
Qimo’s interface has been designed to be intuitive and easy to use, providing large icons for all installed games, so that even the youngest users have no trouble selecting the activity they want.
As a parent of young kids I am always up for something that will help my kids make wise choices online and still allows them to learn and grow.