Just wanted to put this out there- I haven't really researched it enough to know the reasoning...
My son took melatonin for about a year due to various sleep issues. It helped him fall asleep, but definately not stay asleep, and we did try a few extended release kinds.
Then a behavioral/ developmental pedi (at an evaluation) recommended that we stop due to a family history of depression....
I had been thinking of stopping anyway because it wasn't helping his main issue, staying asleep, and wanted to try some relaxation techniques since a year had passed, and maybe he as more able to do those. So, I don't know what the link is between depression and melatonin, but I wanted to put it out there in case this would apply to you and you wanted to research it more. It really did help sleep onset, so it might be a weighing the benefits issue.