The "educational content" rule?
You mean the Children's Television Act 1990.
It was necessary - and only came in because Reagan wasn't around to shit up the place with his fucking senile insistence that his first decision was right and the evidence was wrong - and proportionate. It was also 3 years before Animaniacs even aired (as the original anon suggested), but it doesn't really mean "you've got to have a ham-fisted history segment". Those kind of PSA shorts were actually broadcaster-mandated, precisely to make it look like deregulation was working - because deregulation had been predicated on the idea that broadcasters wouldn't produce the Tits and Killing Hour and try to use it to sell toys and candy.
The previous attempt to reintroduce the regulatory system - which was only done away with in 1984 - was in 1988; Reagan sat on the bill, which was passed with massive support from Congress and industry, until it expired, because Congress was in recess and he could. He just straight-up King'd himself, exactly as a President was never supposed to do. Absolute fucking senile shitbag, and even when you go back to the way he got into politics - selling innocent people to the HUAC while he was a SAG rep - the man never had any intention of accepting reality.
In fact you only need, as a broadcaster (ie a channel that has a license to broadcast which includes children's shows, rather than any channel with a license) to show 3 hours per week of educational content. Anything more than that is on the broadcaster's part.
The fact that deregulation began with the argument that television is "just a toaster with pictures" should be up there with the internet being "a series of tubes", but for some reason it isn't.