Jim Parsons provides voiceover for the series. In the Season 4 episode "Graduation", Mayim Bialik (as Amy, the wife of adult Sheldon) has a brief voice-over role while Sheldon describes the graduation party for their son Leonard, whom he reveals was named after Leonard Hofstadter and Leonard Nimoy. Amy and Sheldon make their only on-camera appearances together during the series finale in the office of their Pasadena, California home in an unnamed future year, as neither of their children had been born when The Big Bang Theory ended in 2019. Bob Newhart appears as Professor Proton in both series; with the appearance in this series, the character is made to look younger. Iain Armitage (Sheldon), Lance Barber (George), and Montana Jordan (Georgie) make a guest appearance in the parent series in a scene in which a VHS tape recorded decades earlier is played. There are other actors who appear in both series but as different characters. This includes Barber, who had another guest appearance in the parent series as a different character, and Kaley Cuoco who stars in the parent series and makes an uncredited voice appearance in this series, voicing an inanimate object. Elon Musk made cameo appearances as himself in both series, appearing in the sixth episode of the first season of Young Sheldon.