When you check into your WDW resort they usually take an 'imprint' of your credit card to cover purchases charged to the room. Then on the morning you check out you get an invoice popped under your door. If you are happy with it you need not go back to reception, they will automatically charge your credit card for the amount owed. If your children have their own door keys cards you can choose for them not to be able to charge things with them
You would get a better exchange rate using a CC - especially the Nationwide one as you get close to bank rate.
In the past we have used our room key for charging things and then paid of the outstanding balance at Guest Services the following morning each day It gives us the convenience of not having to carry lots of cash or travellers cheques but also the abilty to easily keep a track of what we have been spending
if you charge to the room your CC will be debited on the last mornning of your stay.So if you have any TC or cash left over use them to reduce the bill the night before you leave.If you do the disney cruise you have to have transactions charged to room so make shure you clear any bill the night before disembarkation outherwise your card will be charged
Paulh