It takes a lot more thought and creativity to produce something that can appeal to young ones and adults - each on their own level, but it can be done. And when it is done properly, the longevity of the appeal is dramatically increased. Take Veggie Tales for example. My kids loved it when they were small - all little ones really need is color, action, a few songs and a simple message. However, they still enjoy watching them now that they're older because they appreciate the more sophistocated humor that's been built in.
The pre-PC Sesame Streets did that as well - Jim Henson's original idea was that the program should be an hour of "educational commercials"--short little jingles that stick in your head. I can still remember those little ditties word for word even though it's been a few decades. I think I was 9 or 10 when Sesame Street first came out, but my friends and I thought it was HILARIOUS (and it was!)
It was a sad day for me when my kindergarteners decided that they wanted to divorice themselves from Barney-right down to discarding the Barney undies. Sad, not because I would miss the old purple doofus, but because my 5 year olds felt they had outgrown a program that was supposed to be aimed directly at them.