Here's a review from an Iranian journal. Maybe not the most valid source, but it evaluates a few good journal articles:
http://www.ams.ac.ir/AIM/NEWPUB/13/16/7/0010.pdf
There are no double-blind clinical trials yet. (here's another study linking low magnesium with ADHD, although no causation is suggested:
http://www.ijponline.net/content/37/1/60)
I would search for foods high in magnesium and give your children that rather than a huge dosage of straight magnesium. As with most supplements, you're likely just producing expensive stool/urine because the body is only going to absorb what it needs and then flush the rest.