(Elaborating on a story by Wayne Dyer, quoted here [link now no longer functions].)
Have the class, or your family stand up with the goal of jumping as high as they can. Maybe have a goal on the wall or doorway or something to measure how high to jump. In the first situation, no one can bend their knees before they jump - not even a little! So basically you can only go on your tiptoes. You just can't propel yourself into their air without bending your knees first.
Next have them bend their knees just a little bit and jump again and notice how much higher they can jump then finally allow the students to jump as high as they possibly can and bend as much as they desire.
Point out to them that the only way to reach and jump high is to bend low first. So when we are brought low with trials or difficulties we must remember that it takes that bending low to propel us higher. If we are brought low with trials, then we can build sufficient faith and trust in God so he can lift us to a higher spiritual place. There are many stories in the scriptures then that can illustrate this concept.