Check out this interesting research on the effects of poor sleep on insulin sensitivity. Basically, you are more likely to get metabolic syndrome or even diabetes if you have persistently poor sleep.
Moral: if you can do something about poor sleep, then do it, because the consequences of inaction are more extensive than we thought.
And the above leads to faster cognitive decline!
See this article.
Further evidence for the link between omega-3 fatty acids (oily fish etc.) and better sleep - very relevant for children and teens too, I suspect.
Here it is.