The teen looks like he could get away with being The Boys' pubescent Karl Urban, and that would explain why the ghost pleads, "For Becca..." The Boys have an opportunity to dig deeper into the relationship between Billy and Lenny Butcher, explain why Hughie is so important to Butcher in the present, and ask if his soul is still redeemable after injecting V-24 and becoming the very thing he swore to fight. Butcher contemplated injecting the green substance after hiding the V-24 in a bulldog tin, but was deterred by a series of ghosts.
After seeing Homelander, Butcher hears a boy say, "Butcher, you have to stop" before turning around and watching the kid on TV. Billy idolized Lenny when they were children, but the younger sibling took his own life because of their father's abusive behavior, as revealed during a visit to Butcher's Aunt Judy.
It goes against everything Butcher stands for when Maeve gives him stolen samples of V-24 from Vought's labs. In The Boys season 2, Aunt Judy pointed out how much Hugh Campbell reminded Butcher of his late brother, and this first line sounds like it's spoken by Jack Quaid's Hughie.
The Boys season 3, episode 2 dropping a random youngster credited under a vague name like "Teen" surely indicates the boy's identity will be revealed in a later episode. Jack Fulton's character appears again, this time outside of a TV screen, if The Boys gives a flashback to Billy Butcher's early years. The boy in Butcher's dream is around the same age as Lenny was when he died. He first saw the mocking face of Homelander, and then an unidentified teenage boy appeared and begged for Becca. Butcher has a plan to kill Homelander using the same weapon that ended Soldier Boy's superhero career. The washed-up has-beens won't give up their ex-leader's secrets without a fight if he tracks down Payback.
Young Jack Fulton might be playing young Billy Butcher, given the British accent. If Butcher thought so highly of his brother, it makes sense for him to beg him not to inject the V-24. Jack Fulton is credited as "Teen" for portraying the character.
Billy's kid brother is most likely this person. Billy Butcher is desperate in The Boys season 3. Who is the young teenager in Billy Butcher's The Boys dream sequence? It makes sense that his dreams have Hughie's voice in them. The boys have another clue.