All - how can I share some of my iTunes music (not purchased via iTunes) with my kid? Virtually all of those are ripped from CDs. I still have the CDs but I don't want to rip them all again.
If you and your kid – or actually your device and your kid's device are on the same network, you could simply share your library like this:
Go to your iTunes preferences and click on the sharing tab. You can then choose to either share your complete library, or select a playlist to share. On the client iTunes (your kid's device) your shared library should be visible in the top-right corner.
You can also find further details on this over here: "Share your iTunes library over your home network" (at apple.com)
If you are actually not on a desktop/macbook computer then things are slightly different – but still possible. Then you may want to check out this article: "Use Home Sharing to share iTunes content with other devices"
In terms of technology, the files you're talking about don't have DRM, so you can simply copy them to your son's computer. You don't say what kind of devices either of you are using, but you can right-click songs in iTunes and choose Show in Finder/Windows Explorer to see where your music files are located. Then you can transfer these files to your son using the same methods as any other files.
But whether it is legal to do that depends on where you live and other factors, and in some cases it may be a grey area. I just want to be clear that I can give you technical advice, but I can't give you legal advice. I am not suggesting that you break any the laws where you live.