After WandaVision, Wanda Maximoff, alias Scarlet Witch, became one of the Marvel Cinematic Universe’s most tragic characters. Wanda forced the entire town of Westview into a fantasy she built out of grief over the loss of Vision. In the process, she herself became a victim of her reality-warping powers when she became so engrossed in the fantasy that she struggled with defining what was and wasn’t real. Within the Hex, Wanda not only had Vision, but she also had two children, Billy and Tommy. Though the twins were not real, they were real to Wanda.

https://screenrant.com/scarlet-witch-wandavision-agatha-children-theory/