There are ATMs, but keep in mind the extra fees you’ll be charged.
You’ll do better if you use a debit card, assuming your ATM card is also a debit card.
Another alternative, if you have a credit card and are traveling with a computer is to use the credit card and nightly, go to the credit card’s web site and make a payment for your day’s spending. This way, you won’t have any extra fees or extra interest.
If those options don’t work for you, go with the traveler’s cheques.
And also remember that if you’re staying in a Disney resort, you can charge to your room and then use the debit card to settle your bill, either nightly or on check out day.
I really hope your son gets better fast. If you’re flying, or even driving, it’s going to be a rough trip for him.