We’ve known for a long time that Wiccan and Speed would make their debut in WandaVision. First we heard of them having babies on the set, and then we’d see them at around eight years old (and audition tapes for those leaked), but towards the end of the series they’ll apparently be teenagers when they enter the main MCU timeline.
We know that Lizzy Olsen will appear in Doctor Strange in the Multiverse of Madness, but according to a reliable source she’ll be brining the twins with her as the two older actors cast as Wiccan and Speed in WandaVision are supposed to appear in the movie as well. With America Chavez due to make her debut in the film, that would make at least three future Young Avengers in the Doctor Strange sequel.
The most amazing part is that the two actors have already shot their scenes in WandaVision, will be big parts of the MCU going forward, and no one knows who they are yet.