There are two main merchandise shop across the hall from each other and yes, I would say they are the size of a smaller WDW shop...not tiny, but certainly not huge.
They are good sized, not huge, but not small. The one store is more adult clothing, jewelry, bags etc. The other is geared more towards the Kids (in all of us) - they have the pins to trade, photo albums/frames, stuffed animals, more casual tshirts etc. We enjoyed the shops, you could tell by our Room Statement at the end of the cruise They of course are not as big as the one in Downtown Disney, but decent sized for being on a Cruise Ship.
I agree with the other 2 posters about the sizes of the shops on the ship. And one good thing to know is that if there is something that you see and like, but they don't have your size out then ask. The DH found a shirt he liked, but they didn't have his size on the rack, so when he asked they got him one from the back in the right size.
Make sure and check out the store at Castaway Cay...they have some really neat stuff there...a lot of it (or most of it, I should say) is only available there on the island.
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