I just wanted to share that I recently set up my Color Classic (with an LC 575 motherboard) for my 3-year-old daughter to use. I've installed several educational programs, and she loves it. The computer is an ideal size for her, and lets us keep our "everyday" Macs out of harm's way (though she is well-behaved, and we don't let her use it unsupervised or too much).
Our neighbor who has a kid the same age was really impressed with it, and couldn't believe it had a color screen.
So, I've found this to be wonderful, practical use for a "vintage" Macintosh. What 20-year-old PC is this much fun or would have a 3-year-old excited to use it?