Common Sense Note
Parents need to know that this classic '70s educational show is still a lot of fun, if a bit dated. For instance, some of the words that kids are taught (like "reducing exercises") don't really translate today. And in our PC culture, the word "gag" -- while admittedly chock-full of "g" sounds, feels like an odd one to use (accompanied by a human demonstration no less) in this context. It's also worth noting that the show doesn't transfer very well, digitially, to today's HD TVs. Dramatic effects created by having actors work in front of a black screen become fuzzy and hard to watch, as do many of the show's signature "electric" word bursts. If you have an old TV hooked up to a DVD player, that's the way to go.
Occasional borderline innuendo -- for example, Gloria the Glowworm finds Glen to "make her glow."
The show focuses on teaching kids to read. The cast is quite diverse, and overall there's very little to worry about, though some of the behavior/standards are a bit dated (a cast member smokes a cigar, women tend toward the giggly, etc.).
Drugs / Tobacco /
Bill Cosby smokes a cigar as part of a Groucho Marx reference (something that wouldn't really have been frowned upon in the early '70s).