Warning! SPOILERS for Doctor Strange in the Multiverse of Madness.
Scarlet Witch's kids existing on Earth-838 in Doctor Strange in the Multiverse of Madness is a major mystery, as it points to a completely different life without Vision. The Marvel Cinematic Universe introduced the idea of Wanda Maximoff having kids in WandaVision. The Disney+ series showed Scarlet Witch magically creating Billy and Tommy within Westview's Hex, even though WandaVision's ending saw Scarlet Witch lose them and begin a mission to find them through the multiverse. She does just that in Doctor Strange 2, but their existence in Earth-838 remains an unanswered question.
Doctor Strange in the Multiverse of Madness exploring the multiverse led to a journey on Earth-838, where the main MCU's Scarlet Witch wanted to live. This was because Earth-838's Wanda Maximoff had Billy and Tommy. Reuniting with different versions of her twin boys drove Scarlet Witch's entire story, as she focused singularly on them - ignoring the possibility of also finding a world where Vision and Quicksilver were also around. Doctor Strange 2 ignoring Vision is particularly odd, especially when it comes to the idea that Earth-838's Wanda is living a happy life with her family. However, Vision not existing in that universe makes the presence of Billy and Tommy more confusing.
In the main MCU timeline, Scarlet Witch doesn't physically give birth to her kids, but she does create them as part of the illusion about what her and Vision's lives could have been. It is Vision's death in Avengers: Infinity War and the synthezoid's desire to settle down that serves as the catalyst for everything that happened in WandaVision, including Billy and Tommy's creation. Since Vision isn't in the Earth-838 universe, there must be a different explanation for how Wanda's kids exist. Doctor Strange in the Multiverse of Madness' ending indicates that Scarlet Witch is a single mother. While she could've physically given birth to the boys in this universe, it might also mean that Earth-838's Wanda peacefully created her children.
Between Vision's nonexistence and the good Ultron bots in Earth-838, all signs point to Avengers: Age of Ultron not happening in Earth-838. If that is the case, then most of the trauma that shaped Wanda Maximoff's journey to becoming the Scarlet Witch is different in this universe. It would even seem that Earth-838's Wanda decided to settle down in suburbia on her own, potentially never becoming a superhero. Doctor Strange 2's The Illuminati are powerful enough to stop Thanos in this universe after all, so she could have been left alone to live a peaceful life. In that case, creating two children out of magic might have been allowed.
Based on this possible explanation, Wanda's kids existing on Earth-838 points to her potentially having an even greater grasp on her powers than Earth-616's version. Doctor Strange in the Multiverse of Madness points to this version of Wanda being able to create Billy and Tommy without the restriction of the Hex. This possibility was teased in WandaVision, in fact, as Agatha Harkness mentioned she could fix Wanda's spell and make this a reality if she had Chaos Magic powers. Since Billy and Tommy exist in Earth-838, perhaps Doctor Strange taught Scarlet Witch how to control her powers better, resulting in her getting the peaceful life with two kids she wanted - that is until Earth-616's Scarlet Witch used her to kill The Illuminati, potentially making her that universe's biggest villain.
