There have been rumblings for several months (if not longer) that Joe Locke will play Wiccan in Agatha: Coven of Chaos, but his role as "Billy" now appears to have been confirmed by the actor's stand-in.
Billy is, of course, the name of Wanda Maximoff and The Vision's son. Alongside his twin brother, Tommy, they were wiped from existence when the Scarlet Witch took down the Hex surrounding Westview in WandaVision. While comic book fans know that their teenage counterparts are the Young Avengers known as Wiccan and Speed, it's not quite that simple.
When Wanda lost her children in the comic books (after creating them through Chaos Magic), their souls inhabited Billy Kaplan and Thomas Shepard. So, they both are and aren't the Avenger's kids, but thanks to their "mother," the duo were granted incredible powers.
Just like what we saw in WandaVision, Wiccan is a powerful magician while Speed has his uncle Quicksilver's powers.
Presumably, something is going to happen that leads to Agatha tracking Billy down in Agatha: Coven of Chaos. Perhaps she wants his abilities for herself or hopes to train the boy in an effort to make things right after previously crossing paths with Wanda. It depends on whether she's remaining on a villainous path or will find redemption in this spin-off.
Marvel Studios appears to have no concrete plans for the Young Avengers in the MCU. Instead, it seems these younger heroes will just form part of the next generation of Earth's Mightiest Heroes once we bid a final farewell to the original six at the conclusion of the Multiverse Saga.
Agatha: Coven of Choas is currently expected to premiere on Disney+ sometime in 2024.