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
After hearing the full story, McGonagall is furious at how stupid Scorpius and Albus have been. She tells them that they are in detention for the rest of the year, with no visits to Hogsmeade or breaks. Suddenly Hermione bursts in, and McGonagall tells her that it was also incredibly stupid for her to keep a Time-Turner in a place that the boys could find it.
McGonagall acknowledges here the danger of keeping a Time-Turner, perhaps even being more aware of the consequences than Hermione because of the problems that Time-Turners can create.
Active
Themes
McGonagall continues her tirade, saying that after all that Dumbledore did, she couldn’t live with herself if it had all come undone. While Albus and Scorpius’s intentions to save Cedric were honorable, and they acted bravely, they had no idea how dark the world could have become and how much people sacrificed to prevent that from happening. She tells them all to get out and find the Time-Turner.
While McGonagall acknowledges the value in the sacrifice that Albus and Scorpius were trying to make, she also confirms the idea that trying to affect the past (or, in a less hypothetical scenario, thinking about what might have been) is dangerous and unproductive because it could always change for the worse, not for the better.