I'm really sure.
When you check-in at your resort, each person 3 and older will get a credit card-looking-thing. That's Your Key to the World card. On there will be encoded your room key, your park admission media, and your dining credits. You can also set up a room charge that you will access with that same card.
it's very convenient that everything you need is all in one card. And if you lose it, there's no problem. You can get it replaced at any Guest Services location (resorts, parks, DTD). Your room number isn't on there, so it's not like someone can go ransack your room. And even if someone did manage to charge on it, if you have the room charge backed up with a credit card or debit card you won't be liable for any fraudulent charges.