In 1975, she married her android teammate Vision, later using borrowed magical forces to make herself pregnant, resulting in twin sons William ("Billy") and Thomas ("Tommy").
She created them with magic. She probably had dreams about them, so she made them look like Wanda's kids from Earth-838 (they are real). Her kids (made in the Hex) are not real in the MCU universe, or any other universe. They were real in the Hex and when she took it down, they stopped existing.
Meet the happy family. In the comics, Wanda and Vision get pregnant through magic — since Vision is a robot, that's seemingly their only option. They have twins named Thomas and William.
In the show's third episode, Wanda and Vision's little suburb comes to life in color as we move into a Brady Bunch–style homage to 1970s TV and they confront the realization that Wanda herself is bringing some children to life with an unexpected and accelerated pregnancy.
Before there's even time to catch your breath, Wanda is ready to give birth. Geraldine is there — just in the nick of time — to help Wanda deliver a baby boy. Vision arrives after the birth.
How Doctor Strange in the Multiverse of Madness Should Have Ended
Who is Wanda's baby daddy?
Over the course of just six episodes of WandaVision, Wanda Maximoff and Vision moved into a new home together; Wanda became pregnant and gave birth to twin boys; the twin boys aged 10 years; the Maximoff family got a dog named Sparky; the dog died; Wanda's brother returned from the dead; and Vision nearly died (again).
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.
Wanda's magic was the only thing keeping her children alive, as when she concentrated on using her powers for anything else, they'd disappear. (Much to the shock of many a babysitter.) Eventually, Mephisto came to reclaim the shards of his soul, and Wanda's twins, Billy and Tommy Maximoff, were destroyed.
This is supported by the Marvel Comics origins of the twins, whom Wanda creates by unwittingly summoning two pieces of Mephisto's soul. The ancient demon Mephisto later reabsorbs the twins, driving Wanda insane, which loosely resembles Wanda's arc from WandaVision to Doctor Strange 2.
Obviously, Wanda couldn't naturally have become pregnant that quickly, so it seems likely that it's not a “real” pregnancy after all – instead, it could be part of the illusion she and Vision are currently living in.
Vision uses the brain patterns of Wanda Maximoff, AKA Scarlet Witch, for their mother, Virginia's mind, then creates the children from a combination of both his and hers. Viv shares her father's powers and ambition to be ordinary.
Doctor Doom, another dominant personality in Wanda's life, desired her powers for himself, and betrayed her when she sought him out once to help her uncover missing memories.
She realizes she wants to have children with her husband, Vision, but due to him being a synthezoid, they can not conceive naturally. Instead, she uses her powers, powers that, at the time, she neither fully understood or knew how to control, to create two children: Billy and Tommy, the future Young Avengers.
She willed them into existence because of her dreams. So that means that Vision having died had nothing to do with her not having any children, so nothing was taken from her.
Wanda and Vision's kids experience something similar in the comics. Wanda unwittingly made a deal with the devil, named Mephisto in the Marvel comics, to have them. The devil rescinds on their agreement and makes them disappear for awhile, but then they reappear in the stories as teenagers.
In response, Wanda magically creates two twin sons to complete their nuclear family. They were born in 1986's The Vision and the Scarlet Witch Vol. 2, #12.
They're still very young, so it's likely that their powers are still developing. Wanda's inability to control Billy and Tommy reflects something much deeper than the trials and tribulations of motherhood.
We never see Vision or any other partner/father in another universe, so it's unclear where the “real” Billys and Tommys come from, only that Wanda-616 dreams of them often enough that she is convinced they exist for real in other universes, and she's right about Earth-838 at least.
Olsen also added that her character's accent “hasn't gone anywhere”, and that Wanda merely phased it out as she moved to the United States. “There have been reasons for everything,” Olsen explained.
Wanda was neither an evil being nor was she the real antagonist. Wanda was only a villain because the Darkhold corrupted her. Compared to the threat of a Sinister Strange in the making, the Scarlet Witch was only grieving on her terms.
The very same Mind Stone was also responsible for Vision's sentience and superhuman intelligence. So when the pair first interacted in Age of Ultron, they already had a profound connection that drew them together and potentially sparked their feelings for each other.
Scarlet Witch's power goes beyond what Doctor Strange or any other character in the MCU could imagine, so with that in mind, she might have been more resistant to other physical consequences of the Darkhold, as is the third eye.
In the comics, Magento was Wanda's biological father, but Marvel writers have recently undone that storyline. It was revealed that Magento was lying to Wanda and Pietro in the comics all along, and he actually wasn't their father but instead using the supposed family ties to use them.
