Marvel Studios paid off Hulk had a son, Skaar, from his time on Sakaar before Thor: Ragnarok. The surprise appearance of Hulk's son is significant for the MCU's future, but it also has a direct connection to Bruce's story in Phase 1.
When The Avengers introduced Bruce Banner, the brilliant doctor was living in India when Black Widow arrived to recruit him to the Avengers. The interaction between Bruce and Natasha Romanoff included a subtle but heartbreaking tease that he wanted kids. When Bruce is standing near a baby's cradle, he says, "Well I don't every time get what I want." While his line was in response to Natasha asking if he wanted to break his streak of not becoming Hulk, the scene also teased that Bruce desperately wants children. Now that Hulk's son has ed the MCU, Phase 4 managed to give Bruce what he wanted most of all in The Avengers.
Why Bruce Banner Can’t Have Kids (But Hulk Can)
Bruce Banner's inability to have kids was teased in The Incredible Hulk when he and Betty Ross were in a hotel bedroom. He told Betty that they had to stop kissing because his heart rate was getting too high, which would trigger a Hulk transformation. The implication was that Bruce Banner is incapable of having sex without turning into the Hulk at some point. It is quite clear how disastrous it would be for Bruce's sexual partner if that happened. It also is plausible that Bruce Banner was afraid to have kids due to the possibility of ing his Hulk DNA onto a child.
Even though Bruce Banner might not be able to have sex or have kids, the confirmation of Skaar proves that Hulk can have children. The explanation for Hulk having kids comes down to him finding a suitable partner to procreate. Hulk's son Skaar proves that the Jade Giant found one during his time on Sakaar before Thor: Ragnarok. In the comics, Caiera the Oldstrong became Hulk's wife and gave birth to his children. The MCU has not confirmed who Skaar's mother is, but it is possible that Caiera and Hulk's romance also occurred off-screen.
Phase 5 Could Introduce Another Secret Hulk Child
Now that the MCU has already given Bruce Banner one Hulk son after The Avengers, there is also the chance that another secret child could be introduced in Phase 5. Hulk has fathered two other children in the comics. His only daughter Lyra exists in an alternate reality after Thundra stole Bruce's DNA, allowing Lyra to become She-Hulk. However, Hulk also has another son, Hiro-Kala, who is Skaar's brother. He could potentially be the villain of a World War Hulk movie in Phase 5 or 6. Hiro-Kala was also born out of Hulk and Caiera's marriage. Hulk's second son does not have his green skin or a Hulk-like form, as he instead is powered by New Power.
