Ask the girls what their favorite candy bar is. Mention how much you love Reese Cups - ask the girls why Reese Cups are so delicious. Tell the girls that you have this great recipe for home-made Reese Cups. Say you want to make some right now! Have the ingredients in a bag or box, but leave out the chocolate. Have a bowl, spoon, peanut butter, butter, vanilla and powdered sugar and the little paper liners and a muffin tin. Let the girls point out that you forgot the chocolate.
Ask the girls how a Reese Cup is like a marriage/family. (Peanut Butter = Mother, Chocolate = Father, different but complimentary)
Have some Reese's Cups to give out. You could add toothpick flags to put into the Reese's Cups. Just cut out, fold in half, and tape or glue to a toothpick.