Preheat oven to 350°F. Coat a 9 x 13-inch baking pan evenly with cooking spray.
Press the cookie dough into the pan with your fingers until it covers the bottom of the pan completely (make sure the dough touches the pan on all sides).
Bake at 350°F for 15 to 20 minutes, until cookie dough is lightly browned.
Let the baked cookie dough cool for 10 minutes.
With a pizza cutter or sharp knife, cut into 9 to 12 pieces (depending on how large you want your cards to be). Let cookies cool in the pan for another 20 minutes.
Set out bowls of candy decorations for kids to choose from. Carefully place the cookies on your work surface.
Using a blunt knife, cover each cookie top evenly with the frosting.
Using the red decorator icing, write a personalized message, such as "I Love You," on each of the frosted cards. Decorate with candies. Let dry before giving sweet greetings to your favorite valentines!