LitCharts assigns a color and icon to each theme in Harry Potter and the Cursed Child, which you can use to track the themes throughout the work.
Parenthood
Time, Mistakes, and the Past
Friendship, Family, Love, and Bravery
Reputation and Expectation
Death and Sacrifice
Summary
Analysis
Back at St. Oswald’s, Harry, Hermione, Ron, Draco, and Ginny look around Delphi’s room. They realize that she must have used a Confundus Charm to fake being Amos’s niece and a nurse there; there’s no record of her at the Ministry. When Ginny unscrews a lamp, they hear Parseltongue. Harry says in fear that he hasn’t been able to understand Parseltongue since Voldemort died, but now he can again. He speaks in Parseltongue back, and suddenly the walls reveal painted snakes and the prophecy: “When spares are spared, when time is turned, when unseen children murder their fathers: Then will the Dark Lord return.”
As Harry and the others understand more about who Delphi is, Harry begins to recognize the mistakes he’s made with Albus. He’s been so haunted by and fixated on his past—at the prospect of Voldemort returning and harming his family again—that he hasn’t been able to clearly see the danger that has been right in front of him the whole time.
Active
Themes
Harry and the others realize in horror that Delphi must have the Time-Turner and that she’s using Albus (the “unseen child”) and Scorpius to fulfill the prophecy. They then see more words written on the walls: “I will rebirth the Dark. I will bring my father back.” They all understand then that Delphi is Voldemort’s daughter.
The reveal that Delphi is Voldemort’s daughter illustrates her own preoccupation with changing the past—using the Time-Turner—in order to try and bring her father back into her life and escape the childhood trauma that she endured. Additionally, the prophecy acknowledges Harry’s difficulty truly understanding Albus in calling him the “unseen child.”