While the two shows are wildly different in tone and story, the spinoff actually included a couple of references to the original program. In addition to showing the parts of Sheldon's family and childhood that fans recognized, Young Sheldon also had a trio of little nods that you might have missed if you weren't paying close attention.
The first came as a reference to one of Sheldon's childhood heroes, Professor Proton. Grown-up Sheldon always talked about the scientific TV host, and he had a chance to meet his hero when Bob Newhart guessed starred as the character on a couple episodes of Big Bang Theory.
At the beginning of the episode, Sheldon couldn't find his bow tie before his first day of school. He went into a panic, saying that he needed the tie because, "Professor Proton wears a bow tie!" Sheldon was also seen watching Professor Proton on TV later in the episode.
The second major Big Bang reference came in the form of one of Sheldon's other heroes. When Sheldon was seen in his bedroom, a Stephen Hawking poster was on his wall. In the season premiere of Big Bang Theory, which aired just before Young Sheldon, the character asked Stephen Hawking for his blessing before proposing to Amy.
Finally, there was a reference to Sheldon's bragged-about perfect pitch. While he's not a musician, Sheldon likes to tell people that he has perfect pitch, and Young Sheldon showed the first person that told him about his gift.
As Sheldon walked through the halls of high school, he heard a music teacher playing a song. Without thinking, 9-year-old Sheldon played the piano along with her, and she mentioned that he had perfect pitch.
In typical Sheldon fashion, he declined the teacher's offer to pursue music because, as he put it, "Musicians take drugs."