In the comments field type in 'Rated G' for songs that meet your requirements. Then, simply create a smart playlist that looks for "Rated G" in the comments field.
Now, when my daughter asks to use the iPod, I simply choose that play list and I worry a lot less.
[Editor's note: Looking at this hint in from a general perspective, using the comment field and creating playlists based on comment search results offers a lot of possibilities...]

