In the Faith in God book under Serving Others, there is the following requirement: Plan and hold a parent-child activity, such as a dinner, picnic, hike, day trip, or service project. My ward did a Mother-Daughter CupCakeWars activity and it was great! I thought it could be super fun for the girls to plan this themselves.
Maybe you can spend about 20 minutes at the end of an activity to let the girls plan the CupcakeWars as their next activity. They can totally plan how they want to do it… but you can help them out by providing the invitations that they fill out, deciding what they want and making assignments (perhaps have someone prepare the cupcakes ahead of time, but have them ready to be decorated) and once it’s time for the activity, they can fill out the food cards and make sure they have everything. Then they can decide how they would like the cupcakes to be judged... maybe the Activity Day leaders can be the judges, or maybe the girl's can invite the primary presidency or their primary teacher.
I made two invitations:
Have the girls fill out the assignments and staple their little assignment paper to their invitation. Have them also make a master list for the leaders so someone knows what everyone is bringing:
Here is a list of things to remember/ideas:
Lots of Candy - gummy bears, gummy worms, sweedish fisth, sour patch...
Fruit - raspberries, strawberries, blueberries, banana....
Either prepared ahead of time or right at the beginning of the event, have the girls fill out the food labels to put on the table:
Have each Mother/Daguther/Friend team make up a name for their cupcakes. That way the judges won't know whose is who, but can announce a winner using their team name. Have them place their "name table tent" right next to their cupcakes.
And then have these awards ready... let the girls choose whether they want the judge to do "first, second and third" or "most appetizing, most colorful, most unique, most creative". I also made one that says "awesome" in case every girl would like to get something. As the leader, maybe you can even purchase prizes ahead of time for the winners.
You can get my files for this activity HERE :).