The other morning I walked out to my five year old watching Robot Chicken. This isn't what I would call the highlight of my parenting career, but it did leave me with an immediate need to come up with a solution to stopping the kids from watching inappropriate things now that they're big enough to work their way through the MythTV user interface without our assistance. Its now quite common for me to wake up in the morning and discover that the kids have turned the monitor on in the living room, have found one of their shows, and are happily watching. (I guess it says something about the ease of use of the MythTV user interface that my four and five year olds have no trouble navigating it without assistance. Specifically, the video thumbnail of the various recordings is a killer feature because it helps kids who can't read yet find the shows they want.) The animated thumbnail of the recording appears in the bottom right of this example image. Back to my need to filter recordings. Unfortunately this isn't covered in the MythTV book (Amazon), mainly because it didn't seem to me to be a killer feature at…