While Mickey’s Mates sell items primarily aimed at the younger cruiser, Treasure Ketch is aimed more at adults. Here you will find OTC medicines, magazines and books, adult clothing, duty free fragrances, jewellery and so on.
While you are onboard, you use your room key to purchase all items and the total goes on your stateroom account, no cash changes hands. You might like to disable onboard charging going onto your child’s room key. 🙂
Stores on the Disney Magic I believe are much the same (or at least they were last time I cruised on the Magic). The Disney Fantasy and the Disney Dream being larger ships, have much bigger stores so have a wider range of items available, but probably most of the items you see here would be available (excepting the destination specific items).