Ahoy there, Tammy!
Great to see another great question from you. I'm sure your whole family can't wait to go on your summer vacation -- you'll be enjoying sunny warm weather soon!
My family and I are used to using lanyards throughout our voyage to keep our Key to The World Cards handy. We've never lost a card yet -- and having it on a lanyard makes it easily accessible, since the clear plastic pouch has a zip closure on top to easily take the card in and out. You'll need to take out the actual card and swipe it whenever you make a purchase onboard or if you are taking a photo with one of the Disney professional photographers. Also, when you are back in your stateroom, hanging the lanyards on one of the hooks is also is a nice way of keeping cards from getting lost inside your room.
When you get on and off the ship at a port of call, you'll always need your Key to The World Card plus your ID or Driver's License. You won't need to swipe your card when you are exiting the gangway or re-entering the ship though. They have different machines there and you can just tap your card thru the plastic and the machine reads it for identification purposes. The plastic pouch on the lanyard will keep your ID & Card both safely.
If you are a DVC member, stop by the DVC desk onboard since they usually give out lanyards. You can also purchase one of many Disney designed lanyards at one of the
onboard shops. There are quite a few cute ones to choose from.
Wishing you a magical voyage in June, Tammy!
~ Dolly