We're not aware of research suggesting that kids should not take vitamin & mineral supplements ...
However, our products have been specifically formulated for adult men and women & we have to recommend you speak with your healthcare professional for an appropriate supplement routine for children.
As an example, the daily recommended dietary intakes for magnesium vary between age groups, as per the below from the National Institues of Health:
1–3 years: 80 mg
4–8 years: 130 mg
9–13 years: 240 mg
14–18 years: 410 mg (men) / 360 mg (women)
18+ years: 400-420mg (men) / 310-360mg (women)
Apologies we can't be of more value here, it's just that kids needs can definitely vary to adults & would hate to give wrong advice.