Sleep shapes mood, attention, appetite and immunity. For most children the problem is not the amount of sleep available but the consistency of the run-up to it.
Keep the same order every night: bath, pyjamas, teeth, two books, lights out. The predictability itself is the sedative.
Move screens out of the last hour. Blue light and stimulation both delay the natural drop in alertness that makes falling asleep easy.
Hold the wake-up time steady, including at weekends. A stable morning anchor does more for bedtime than any bedtime rule.