On the tenth season of “The Big Bang Theory,” Sheldon spoke about how his habit of knocking three times came from when he walked in on his father sleeping with another woman at 13, something that has stayed with him since. In Episode 11 of the sixth season of “Young Sheldon,” titled “Ruthless, Toothless, and a Week of Bed Rest,” Sheldon’s twin sister Missy, played by Raegan Revord, who is also now 13, confronts their father, George Sr., played by Lance Barber, about having an affair with their neighbor Brenda Sparks, played by Melissa Peterman.
However, on the show, George and Brenda haven’t slept together yet. There have been signs of the two having feelings for each other, but while it was inching towards a full-blown affair, that hasn’t happened yet. And with Missy’s confrontation, any plans the two may have to act on their feelings are sure to be delayed, assuming it happens at all. This means that a formative part of Sheldon’s childhood is unlikely to occur in “Young Sheldon” when it reportedly occurred in “The Big Bang Theory.”