A child's internal clock is set by light, not by willpower

Newborns barely have a circadian rhythm at all; it forms at around three to four months. After that the main tuner is light: bright daylight says awake, darkness lets melatonin through.

So the routine that actually works is unglamorous and physical. Daylight and a walk in the morning, dim lights in the evening, the same wake-up time every day - including weekends.

What knocks the clock out: a schedule that changes daily, bright screens late, and time zones. And if the rhythm has already slid, it moves back at about fifteen minutes every two or three days, not in one night.