I do know that w/o sufficient magnesium and vitamins D in the blood, calcium uptake is not as prolific.  You need a ratio of 1:2 magensium to calcium for uptake to the bones etc.  Now when you consider really that when cortisol levels are too high these kids calcium uptake plummets, you can assume automatically from that that this is not for the lack of calcium in the diet.  It’s the acidity of the blood and the lack of the former supplements in the blood that effects whether they get enough calcium or not.  

It’s not like we can even do anything to change the blood chemistry or the cortisol levels when they are on a certain dose and especially if they are sick.  As they say, it’s better to err on the side of safety.  What I can say though is that you really need to make sure that the caclium tablets you give your kids have both magnesium and Vitmain D in them, or a lot of that calcium is just excreted.  Exactly how much magnesium they can "retain" though when their meds are simply too high for them is anyones guess as if cortisol levels are higher, no matter what amount of that mineral you take, your body will only hold so much of it dictated by your blood acidity and the rest is excreted also.