Captain America is the father of Peggy Carter's kids in the Marvel Cinematic Universe, according to Avengers: Endgame writers Christopher Markus and Stephen McFeely. Throughout the 22-film story of the MCU, people like Marvel Studios head Kevin Feige and directors Anthony and Joe Russo have received a lot of credit, and rightfully so. The Russos made their mark with a focus on Captain America, as they directed his final two solo films.
Joining them throughout this journey have been Markus and McFeely, who created Agent Carter and have been the writers on the entire Captain America trilogy, Thor: The Dark World, and both Avengers: Infinity War and Avengers: Endgame. Thanks to this long history with the MCU and Captain America, they were the perfect fits to bring Steve Rogers' arc to a close in Avengers: Endgame. They did so by having him go back in time and live out the life he always wanted with Peggy Carter. The implications of this have been debated, as Markus and McFeely disagree with the Russo brothers' explanation.
Their belief is that an older version of Captain America has always been around as the MCU has unfolded, which can be believed given how few details they revealed of Peggy's past without Steve. One of the pieces of information that was included in Captain America: The Winter Soldier was that Peggy had two kids with her mystery husband, and in an interview with THR, Markus and McFeely said that those kids are indeed Steve's.
McFeely: It was always our intention that he was the father of those two children. But again, there are time travel loopholes for that.
Markus: It does introduce the idea that there are two children who have somewhat super soldier DNA.
If this really was Markus and McFeely's original intent for Captain America's arc, then this really was a great job on their part of seeing their vision through. They did all they could in the films to make this possible, but stopped short of actually writing in a scene that showed Steve and Peggy with their full, happy family. That said, the writers are admitting that this is just their intent with Captain America's story, and the conflicting ideas between them and the Russos makes it impossible to know right now which explanation is actually canon in the MCU.
Should Marvel Studios eventually confirm that Markus and McFeely's intent for Cap's arc is the canon - meaning that this is all part of a big closed time loop for him - then it would also mean that there are two other people in the world with super soldier DNA to some extent. Peggy and Steve had one boy and one girl, but their ages are never specified. It is most likely that they were both born in the 1950s, which would make them around 80 years old in the present 2023 MCU timeline. Whether they actually look that old or are somewhat younger thanks to the serum's capabilities, it would be quite surprising if future MCU movies explore this new wrinkle. Instead, Captain America being a father just makes the new life with Peggy that he found at the end of Avengers: Endgame all the more fulfilling and rewarding for him.
Source: THR
