
In Marvel Comics, Reed Richards and Sue Storm have two children: Franklin and his younger sister, Valeria. However, the mid-credits scene in the MCU's The Fantastic Four: First Steps suggests that Franklin and Valeria's characters have been mashed together, with the boy adopting some of his sister's most prominent traits and plot points in the comics.
Warning - The rest of this article contains spoilers for The Fantastic Four: First Steps.
In the mid-credits scene of First Steps, audiences see Vanessa Kirby's Sue Storm reading a children's book to her now four-year-old son, Franklin. When they finished with it, he asked for another. As she fetched one, HERBIE, the team's helpful robotic and unofficial fifth member, suggested Charles Darwin's The Origin of Species. Sue turned the suggestion down, noting that while it's one of Franklin's favorite books, he's already read it.
While Franklin had an above-average intelligence in the comics, he wasn't anywhere close to a super genius, especially so young. That distinction belonged to his sister, Valeria, whose intelligence as a child rivaled and surpassed even her father's.
So, Franklin's interest in reading the works of Charles Darwin at four years old points to his having Valeria's superior intelligence on top of his reality-bending powers (which make him one of Marvel's most overpowered characters). But that's not the only thing Franklin has taken from his sibling.
When Sue returned with another children's book, she saw Robert Downey Jr.'s Doctor Doom, who, against the odds, managed to debut in First Steps. Doom kneeled before Franklin as the child tenderly touched the supervillain's exposed, presumably scarred face. Doom has never had such a seemingly close connection to Franklin in the comics, with that honor belonging to Valeria.
Does This Mean We'll Never See Reed & Sue's Daughter in the MCU?

In the comics, Sue Storm had another complicated birth with their second child, threatening the lives of her and her daughter. However, they were saved thanks to Doctor Doom's intervention after the Fantastic Four matriarch begrudgingly agreed to allow the Latverian dictator to name her newborn child, Valeria, after his first love and become her godfather.
Doom kept a close eye on Valeria from afar, even secretly influencing her as an infant to the point that her first word was "Doom," to the horror of Marvel's First Family. Valeria eventually grew to genuinely respect her tyrannical uncle for his intellect and for treating her as an equal.

Robert Downey Jr.'s casting as Doctor Doom complicates matters in the MCU, since it's doubtful that the mega-star will stick around as the Fantastic Four supervillain after Avengers: Secret Wars. Leaving one to question whether Marvel Studios will ever use the character again, especially after using arguably his biggest and most iconic story.
Rumors point to a recast after Secret Wars, which would be required to adapt Valeria properly. After all, not even her name would make sense without involving Doom in her birth.
Additionally, the fact that Downey's Doom has potentially been secretly visiting Franklin would lessen his eventual connection to Valeria. However, where his connection with Franklin in the MCU could be nothing but a means to an end, it could eventually be paralleled with a more genuine bond with Valeria as his goddaughter.
Franklin's uncharacteristic intelligence compared to his comic book counterpart doesn't mean that his sister can't be even smarter. Hopefully, wherever the MCU takes Marvel's First Family, they'll eventually have another addition to the family down the line.