NBC stopped airing Saturday Morning cartoons in August of 1992 with the exception of Wishkid. They kept the teen sitcoms and NBA Inside Stuff. They added Saturday Today. That fall, the last cartoons were gone from NBC. In September of 2006, NBC reinstated cartoons and educational kids shows from Discovery Kids. NBC went to educational cartoons produced by Quobo which they run today 3 hours a week giving affiliates 3 hours of EI programs
CBS stopped airing Saturday Morning Cartoons in the late winter/early Spring of 1997 in favor of a Saturday Morning Newscast and 3 hours of live action and educational kids' shows. In the fall of 2000, CBS reinstated EI Cartoons using shows from sister network Nickelodeon. In 2007, they partnered with DIC and still air 3 hours a week of EI Cartoons.
Fox is a bit unusual. They began Saturday Morning Cartoons 3 hours in Saturday Morning and 30 minutes weekdays in September 1990. In September, 1991, Fox expanded to 4 hours Saturday Mornings and 90 minutes weekdays. In 1992 they expanded 2 and a half hours weekdays. In 1993, they expanded 3 hours weekday afternoons with the option of running one of those hours in mornings. In 1994, Fox ended network cartoons. They made the Fox Kids into a Syndicated group of shows giving affiliates right of first refusal.
When New World owned stations took Fox affiliation, they did not take Fox Kids with a couple exceptions in 1994 and 1995. WHen Savvoy though took Fox affiliation on their 4 stations they did take Fox Kids. When Fox bought a couple ABC stations, they too took Fox Kids. Ed Ansin's Fox station dropped Fox Kids in the Fall of 1993 and opted not to take it either.
Initially, Fox Affiliates HAD TO run it if no other station in the market was willing to take it. O & O stations also had to take it. Then in 1996 the policy changed for O & O stations. They then had the option of putting it on another station willing to take it. So Fox's Greensboro station assigned the Fox Kids to the WB station across town. Fox's Birmingham station slated to Take Fox Kids opted to allow the bumped affiliate WTTO to keep Fox Kids being they were not taking a newtork.
In 2000, Fox decided that even if affiliates could not find a station to take Fox Kids, they would no longer have to run it. They then decided Fox Kids was fully syndicated and no longer part of the network at all. The cut back weekdays to 2 hours. In 2000, it was dropped in Birmingham from WTTO and WBRC did not take it. Also weekdays were dropped in Memphis and St Louis that year and not picked up anywhere. Fox ended Fox Kids altogether at the end of December of 2001 and continued 4 hours of reruns Saturday Mornings. In the Fall of 2001 they partnered with someone else and revamped the Saturday Morning programming as Fox Box initially and by 2005, 4 Kids TV. That continued until December of 2008. Fox instead syndicated 2 hours of Marketing Informercials as "The Marketplace starting in 2009. So Fox totally left Kids programs early in 2009.
ABC continued Satirday Morning Cartoons 5 hours a week until 2003. Beginning in 1997, ABC and Disney Channel partnered running mostly Disney Channel shows on ABC Saturday Mornings and all Disney Channel stuff by 2000. ABC added an hour of Good Morning America Saturday Mornings in September of 2004. They cut the Children's shows from ABC to 4 Hours. In 2006, the Saturday Morning Cartoons were cut back to 3 Hours. While partnering with sister Network Disney Channel, the cartoons were less than half and the shows were mostly live action by then. By 2008, the Saturday Morning shows were all reruns. ABC ended this partnership August 27, 2011. They outsourced these three hours September 3, 2011 to Litton Entertainment. These three hours of shows are educational with a couple shows aimed at kids and others aimed at teens.
So CBS and NBC now are the 2 networks left programming Cartoons on Saturday mornings all EI. Fox has no kids programming at all but O & O stations run the same educational Kids shows. Affiliates also must run 3 hours of EI programs but not from Fox. ABC affiliates are given 3 hours of EI shows as well.