Best way to make sure a kid sleeps at night:
- Make sure they get lots of exercise during the day. This is generally impossible at most public schools, so that means get them out of the house and running around after they get home from school. If they are attending a tutorial center or other daycare facility, make sure there are PE programs in place that get the kids out and about. Consider this homework: it is just as important for a child's mental development to get a suitable amount of exercise as it is for them to study books.
- No caffeine within five hours of sleep-time, including (but not limited to) iced tea, coca-cola, or even caffeinated candies, like chocolate or coffee-toffees.
- No sugar within one or two hours of going to bed.
- Make sure they get to bed on a regular sleep schedule, every night; do not vary this. Circadian rhythms are very strong, and if a child habitually stays up 'til 10 on weekends, then you should expect their sleep schedule to be disrupted for at least Monday and Tuesday. Also, don't let the kid sleep much during the day, or oversleep in the morning. If they went to bed late the night before, wake them early the next day and force them to get out of bed -- this reinforces circadian rhythms, and makes it less likely that the child will get habituated to a late-night schedule (like you describe, above)
- A hot bath helps. A lot.
- A bed-time story or other quality one-on-one time with a gentle, calm parent helps. A lot.
- A regular, habitual schedule (bathing, brushing teeth, putting on jammies, glass of water or hot milk, sitting for a story, etc) before bed-time helps. A lot.
If these strategies don't work (and i should first add, they have never failed for me), then other techniques can be used, like breathing exercises, where a parent teaches a child to breathe by filling their lungs to capacity, and then slowly exhaling in a controlled manner.
There are plenty of basic breathing exercises one can find on yoga and meditation sites; there is no need to teach any particular visualizations, or to indoctrinate the child with any dogma. Simply the act of breathing deeply and slowly will provide a tremendous material boost to the child as s/he tries to calm themselves for sleep.
Similarly, one can "play the quiet game", where whispers are used, and every movement is done in a calming, gentle, somnolescent fashion. Believe it or not, children do need to be taught this; as a teacher in Asia, I can testify to the complete inability of the kids over here to whisper; they just don't know how. By playing "the quiet game", a parent can easily teach their kids a lot of useful strategies for calming themselves before bed-time.
If wanted, visualization exercises can also be used; these can be religious in nature (i.e. -- prayers), or non-religious in nature (sometimes called "self-hypnosis", also "meditation").
In short: use common sense. Keep your kids away from caffeine and sugar (especially high-fructose corn syrup, which is what most candies are made of, today); make sure they get plenty of exercise, and work with them to help calm them, and get ready for bedtime.