Schizoid behavior is a pretty common thing in children. It's accepted, because all we adults have this unspoken agreement that children are lunatics.

King’s line uses dark humor to point out how adults normalize children’s erratic, intense, or contradictory behavior—mood swings, imaginative obsession, sudden cruelty or tenderness—by treating it as a temporary, socially “safe” form of irrationality. The provocative term “schizoid” is less a clinical claim than a rhetorical exaggeration meant to expose an adult double standard: behaviors that would alarm us in grown-ups are excused in kids because we assume they will “grow out of it.” The “unspoken agreement” suggests a collective social fiction that protects adults from confronting how strange childhood consciousness can be, and how thin the boundary is between ordinary development and what we label as madness.