When I was 12 I suffered with terrible insomnia. It was triggered by watching something frightening on TV which I shouldn't have seen. Eventually it passed but I remember feeling better if I knew my dad was up! He used to make me a hot milk and read me a story and play a particular piece of music (jazz) that I then used to help get back to sleep. I still listen to it now if I can't sleep!
Dd1 (age 10) has had this for the last two years since she had pneumonia. If she can't sleep then I give her a time she can put her light on and read for a short time. That usually relaxes her enough to sleep as she's not worrying about not sleeping, she's waiting for the time she can read. If there's something important or she's had a lot of bad nights then the GP suggested I give her a dise of piriton.