Because you can't believe everything you read on Wikipedia.
The only "law" I'm aware of regarding children's programming (especially cartoons) is that they have to have a minimum of 65 episodes to be syndicated... so shows that were either originally network shows that had a fairly long run, you'll only see selected episodes from the series in reruns because most distributors aren't willing to pay the extra money to air all the episodes (ala The Chipmunks' Saturday morning cartoon from NBC had an eight year run at 104 or so episodes, but only the first 65, which its first five and a half seasons, were syndicated in reruns); meanwhile, certain shows are created exclusively for syndication, and therefore, produce 65 episodes specifically in one season.
Besides, the programs you mentioned weren't necessarily aimed at just children... keep in mind, these are programs from back in the 60s or so, back then when ALL of television was supposed to be family-friendly. On top of that, they're not aired as children's programming, they're aired as holiday specials. And most of, but not necessarily all of the Charlie Brown specials DO have some educational value to them. Why Charlie Brown, Why? was originally intended to be a five-minute informational film to show to childhood cancer patients in hospitals, before Charles Schulz proposed to turn the idea into a half-hour special for television.