Hi Carol, welcome aboard! I'm so excited for your family that you'll soon be setting sail on your very first Disney cruise! You will each have your own Key to the World card which will serve as your room key and have charging privileges (or not for the kids, depending on what you choose) for the shops and any other extras you'd like onboard. You'll want to have it with you every time you leave your stateroom.
Many people wear a lanyard with a clear plastic pouch at the bottom to hold their card. This way it's right there whenever they need it. Since you're a first time Disney cruiser, you won't receive a lanyard as you board. Those who have sailed with Disney before are part of the Castaway Club, and will receive lanyards when they arrive. I suggest you look on
Disneystore.com or check your local stores to pick up a fun lanyard with a pouch. The Disney Store online even has a really cute Disney Cruise Line lanyard with a larger pocket wallet on the bottom which is nice too!
You'll also find many people just toss them in their day bags that they will carry everywhere on the ship. It's really up to you!
Enjoy the last bits of planning before you set sail, Carol! Have a great cruise!