- a pack of gum or small bag of candy
Ask for a volunteer. Tell them that if they do 10 jumping jacks (or something quick) that you PROMISE (use the word "promise" over and over) that you will give them a pack of gum.
After they have finished, tell them they did a good job but you've changed your mind and only give them 1 piece instead of the whole pack.
Ask for another volunteer and do the same thing over (the kids will say" but you promised!!!" Act very sincere but have excuses for not wanting to give the whole thing.
After, call the same kids up and ask them "How do you feel when you did everything I asked you to do but I broke my promise?"(Give them the rest of the pack)
This is where you explain that the only one that will never break his promise is our Heavenly Father and Jesus Christ. They won't and in fact, they cannot, by eternal law. Hold up the scriptures and tell them it is full of wonderful promises and if we do our part, he will do his. (I also slip in the Temple and how great the promises are there, too.)
For he will fulfill all his promises which he shall make unto you, for he has fulfilled his promises which he has made unto our fathers (Alma 37:17).