One more Operating System just for kids, is Sugar on a Stick, which is a live OS and can be used from a USB stick. This will protect your computer from kids, and kids can use Operating System on any computer they like. This can be used on a computer without a hard disk. Easily available for download.
You’ll need a USB flash drive of a size of at least 1 GB to install space for saving your work and changes to the system.
Another Linux for the kids is Edubuntu. For Pre-school aged children it has many educational and fun games. For teachers it helps them to manage their classroom learning environment with easily installed and usable operating system with minimal fuss. For students it provides best open-source educational software. Edubuntu can be downloaded from their website.