Mineral supplements for kids?

Do you give you kids mineral supplements? What kind?
I've been searching for some for ds, but I'm having a really hard time finding some without vitamins, and without too high levels of minerals.
I've heard about synthetic vitamins being bad. What's the deal with mineral supps? I'm sure diet is better, but are they ok? How hard is it to get the right minerals through diet?

I'm interested especially in calcium and magnesium, for his teeth (he has cavities already)

I did find this site, that has the rda for different ages, AND the upper safe level: http://ods.od.nih.gov/Health_Informa...ct_sheets.aspx
and this: http://www.acu-cell.com/crcu.html

Thanks!!