Upon check-in at your resort, you will receive a "Key to the World" card. It is the same size as a credit card. Each person in your party (You, Wife, Son, & Daughter) will receive one with their name on it. [I usually carry all of the cards around with me, unless our family splits up.)
This card is:
(1) your room key [Any of the four cards will unlock the resort room.]
(2) contains your park tickets [Each person will use their individual card when entering the parks.]
(3) contains your dining plan [At the end of a meal, just hand them one card. They will deduct the appropriate number of credits from your balance for your entire party.]
(4) used at the Fast Pass booths [Each card can only be used once in the Fast Pass booth, so you will need to use each card.]
(5) can be used for purchases (souvenir, etc.) made in the park [if you opt for this by using a credit card at check-in]. [WARNING: There have been reports of visitors that have noticed that their credit cards were charged for meals instead of the dining plan. So, watch your receipt carefully.]