With Linux, you can create a separate account for each family member. People can only modify their own files. If you do not give out the super-user password, you can make it all but impossible for your system to be damaged. Cost Windows is very expensive. In addition, there is much less free software for Windows than there is for Linux, so you end up paying more for applications.
Application support is the one area in which Linux is criticized.
Sanity You've surely heard many stories from frustrated Windows users about how their computers mysteriously stopped working, or needed a re-installation, or how they spent hours fiddling with IRQs and resource conflicts and so forth. Once Linux is set up, you just leave it alone. Amazingly, it keeps working. This alone is worth the trouble of learning Linux. The Windows software which implements this protocol is supplied by the ADSL provider, but is notoriously problematic.