When I was a boy, the comic books had ads with the Cheerios kid. I have some of the same comics today.
The Cheerios Kid had a girl sidekick named "Sue" who appeared with him on television commercials.
I don't know if she was in any of the comic book ads. I don't remember seeing her in any of them.
But the character they originally had to advertise Cheerios was a girl. I don't suppose it was really the same character, but it had some similarities to the later version. She was called "Cheeri O'Leary". And at that time, the cerial was called "Cheerioats".
"The Food Quints" represented vitamins, protein, carbohydrates, minerals, and fat, all things kids needed in their diet. They could have been named after the famous Dionne Quintuplets, who happen to have been girls.
A little boy character who appeared with the little girl came later.
He didn't look the same as the later Cheerios kid, but that might have been where that character came from.
I drew some Cheerios ad parodies with a character that represented me as the Cheerios kid and a girl that was supposed to represent Sylvia Terrel as Sue. There wasn't much resemblance between us and the Cheerios kids, but we had dark hair.
One of them had a gorilla monster in it, because of this commercial.