WARNING: The following contains spoilers for WandaVision Episode 5, "On a Very Special Episode...," now streaming on Disney+.
Wanda and Vision are anything but a typical couple, so it's no surprise their twin sons, Billy and Tommy, don't develop the way other kids do. The pair are only infants when WandaVision Episode 5, "On a Very Special Episode...," picks up, before suddenly aging up to five years old. They do it again later in the episode, sprouting from five to ten years old in the blink of an eye. However, if the siblings suddenly look a little familiar at this age, that's probably because you've seen their actors in a recent movie or TV show.
The ten-year-old version of Billy on WandaVision is played by Julian Hilliard. Although he's only been acting for a few years, Hilliard's already made a splash thanks to his performance as the younger Luke Crain in the flashback scenes from Netflix's 2018 The Haunting of Hill House series. He also appeared with Nicolas Cage in writer/director Richard Stanley's 2019 H.P. Lovecraft film adaptation, Color Out of Space, and co-starred as Peter Craft's son Tom on Showtime's Penny Dreadful spinoff show City of Angels. Hilliard will play a supporting role in the upcoming The Conjuring: The Devil Made Me Do It.
As for the ten-year-old Tommy, he's brought to life on WandaVision by Jett Klyne. Similar to Hilliard, Klyne has appeared in a handful of horror projects, including the films The Boy and Devil in the Dark. He's also made one-off appearances in the TV shows The X-Files, Colony and Supergirl and played a young Harvey Kinkle in the Chilling Adventures of Sabrina episode "Chapter Three: The Trial of Sabrina Spellman." Like Hilliard, Klyne's involvement with WandaVision was confirmed through his Instagram account, both of which are managed by the actors' respective parents.
Meanwhile, the five-year old-versions of Billy and Tommy are played by, respectively, Baylen Bielitz and Gavin Borders. Obviously, being as young as they are, neither of them have really done much professional acting before WandaVision. That said, there's a slight chance you may have spotted Borders as "Young Boy" in the Fred Rogers biographical drama A Beautiful Day in the Neighborhood.
Given their unpredictable nature, it's anyone's guess how much longer Billy and Tommy will remain ten years old on WandaVision or what will ultimately become of them in the Marvel Cinematic Universe. For now, though, they appear to be taking their mom's pep talk to heart about life having rules and the importance of not rushing their aging, just because it's convenient and something they can even do in the first place.
Written by Jac Schaeffer and directed by Matt Shakman, WandaVision stars Elizabeth Olsen as Wanda Maximoff/Scarlet Witch, Paul Bettany as Vision, Randall Park as Agent Jimmy Woo, Kat Dennings as Darcy Lewis, Teyonah Parris as Monica Rambeau and Kathryn Hahn as Agnes. New episodes air Fridays on Disney+.