So most probably with respect to Windows there is only one user, also administator, installed on your PC and you, your kids and your wife use the PC as one account=one user.
Then, also in that situation, still there is the option of making and saving "own" playlists for each individual member of your family. By loading such "own" playlist(s) each member of your family then has its own list(s) of media. I don't think that solution is - in practice (considering what you still have to do yourselves) - so different from what you suggest as a new feature.
