Show the rulers/sticks and tell the children that you are going to make a promise. The promise is that you will put these two rulers about two feet apart and then jump over both of them.

Place the rulers as you said and jump over them. 

Move them a little farther apart and promise again that you will jump over both with one jump. (Make sure that you can keep that promise.)

Spread the rulers wide enough so it is obvious you can’t jump over both in one jump. This time, don’t promise to jump over both in one jump, but ask the children what they would think if you made that promise. Would they be able to trust you to fulfill that promise?

Show that you can’t jump that far in one jump.

When I made the promise and the rulers were close together, you had no problem trusting that I would keep the promise. When the rulers were too far apart, it would be foolish of me to make a promise to jump both in one jump. Even if I did, you wouldn’t trust me to keep that promise.

It makes sense to only promise things that you know you can do. Even then, we sometimes fail to keep some promises. When God makes a promise, though, you can count on it. He will never break a promise, because he can always do what he says he will do.

One of the promises he gives us is in 1 Peter 5:7. God says you can cast your cares on him because he cares for you. 

God is powerful enough to create the world by just speaking the word. If he is that powerful, he can easily take care of any problem you and I may have. 

Note: For your class, choose a promise that fits the lesson you're teaching.