Ok, I am not a parent but I have a younger sibling.
So far to filter movies, I use Movie maker or simply WARP thorough the movie. It works for movies like Jhonny English or Get Smart to remove nudity. However, if it's a movie like Black Hawk down, its difficult to remove swearing without watching the whole movie once and noting down crucial points and then editing audio!
Found some interesting things that you guys may like :
http://www.clearplay.com/
http://forum.doom9.org/archive/index.php/t-67781.html