First make the frosting. Beat softened butter on medium speed with an electric or stand mixer. Beat for 3 minutes until smooth and creamy. Add powdered sugar, cream and vanilla extract with the mixer running on low. Increase to high speed and beat for 3 minutes. Add a little more powdered sugar if frosting is too thin or a little more cream if mixture is too thick.
Divide frosting into 4 bowls. Add a few drops of red to one bowl. Stir to combine. Repeat process with remaining colors (yellow, blue and green). Set aside.
Separate the M&M's into colors - red, blue, green and yellow.
Frost 5 cookies with red frosting, 5 with blue, 5 with green and 5 with yellow.
Place about 12 or 13 red M&M's around the edge of one red frosted cookie. Repeat with remaining red cookies. Then do the same for the other colors.
Meanwhile, microwave the semisweet chocolate chips and shortening in a microwave safe bowl for 1 minute on high. Stir until completely melted. Heat for 15 more seconds, if needed. Pour into a plastic zip top bag. Seal and cut a small corner off. Pipe the messages on your cookies. Then "glue" the air heads on the cookies with the remaining melted chocolate.
Store covered for up to 5 days.