I remember Kelloggs being promoted by Hanna Barbera characters alot.
Post did it too.
Linus the Lionhearted was an animated cartoon created by the Ed Graham advertising agency, originally as a series of ads for Post Cereals. The ads were so popular that a television series was created in 1964 and ran on the CBS network, and from 1966 to 1969 on ABC when it was cancelled.
In addition to Linus, a rather good-natured "King of the Beasts" voiced by Sheldon Leonard, there were other features as well, all based on a popular Post cereal. The best-known of these was Sugar Bear, who was voiced by actor Gerry Matthews. There was also a postman named Loveable Truly, a young Asian boy named So Hi, and Rory Raccoon.
The show was perhaps best noted for its abundance of well-known vocal talent. In addition to Leonard, Carl Reiner did several characters, most notably Linus' friend Billy Bird; Ruth Buzzi did an old woman who'd befriended Loveable Truly, as well as Sugar Bear's sometime nemesis, Granny Goodwitch, and veteran Bob McFadden did So Hi, Rory and Loveable Truly. Jonathan Winters also did a guest appearance, as did Jerry Stiller and his wife Anne Meara.
The FCC made a ruling in 1969 that forbid children's show characters from appearing in advertisements on the same program and this meant that ABC were forced to cancel the program.