Yep - just my added .02 on where a bit of confusion may have arose:
When making the choice between say a jumbo mouse and a very young rat (both items appx the same size) the calcium argument IS valid since an adult of ANY endoskeletal species WILL have more signifcant calcium levels than a similarly sized juvenile. I.E. bitty jr rat vs bigass adult mouse - mouse will have more calcium.
I agree that bottom line appropriate size is key factor.
To supplement just give em flintstones chewables.
(PLEASE don't take that last line seriously - snakes do not chew and certainly don't give them human vitamins)