During the early 1960s, a lot of cartoons were broadcast during prime time, for audiences of both kids and adults: Yogi Bear, Beany and Cecil, Rocky and Bullwinkle, Top Cat, The Alvin Show. The Flintstones, which premiered in September 1960 at the rather late hour of 8:30 pm, went even farther, with decidedly "mature" plotlines.
a mysterious foundling child who might be an alien.
There were no supporting characters, only a few recurring characters. The camera was focused squarely on the dynamics of the heterosexual nuclear family.
At first, the plots were mostly about misunderstandings, squabbles, and conflict: Fred and Barney want to go bowling instead of going to the opera with their wives; Fred and Barney secretly take dance lessons, but their wives think they are seeing other women.
The wives became so irrelevant that you could buy toy sets with figures of Fred's car and Dino, his pet dinosaur, but not Wilma and Betty
After the initial series (1960-66), nine more Flintstones series aired, mostly on Saturday mornings. Some involved Pebbles and Bam-Bam as teenagers, and others involved Fred and Barney by themselves. Wilma and Betty barely mentioned, or not mentioned at all. In the juggernaut of advertising tie-ins that continues to this day, we similarly see no Wilma or Betty, just Fred selling Flintstones Vitamins or Barney trying to trick Fred out of his Pebbles Cereal.
See also: Yogi Bear and The Three Stooges.