The Stewie Griffin fan theory puts a spin on the seemingly normal family dynamics. Redditor u/Jacob_Wallace_8721 kicked things off in the thread “The animated actor for Stewie Griffin is actually the eldest sibling and is just very short.” They noted how in the Season 15 episode “Inside Family Guy,” it’s revealed that the comedy we know and love is really a “show within a show” and that while Stewie plays the youngest of the Griffin brood, he’s, in reality, a little person and the oldest of the bunch.
To elaborate on the theory, they wrote, “Stewie acts the most adult, being openly gay, pursuing lovers, and has his own side businesses going on. He also has the deepest voice … When developing the show as a family, they just thought it would be funnier if he was a baby in the show. It also makes the sex jokes less creepy, as everyone in universe would know he’s an adult.”
They even defended their position by saying it’s plausible that Stewie is the oldest child because Peter and Lois are in their mid-40s.