Michael Wilcox, a member of the Stake Presidency in Draper, Utah, gives this analogy at each stake baptism:

(this is from memory after hearing him give it once - March 3, 2001)

        First he called the children who were being baptized (there were four this time) up to the stand.  He had a small square container of sand (like a tupperware container that holds one sandwich).  He talked to the children about how when they play in the dirt all day, they get dirty and sometimes the dirt sticks to them and their clothes, etc.
        Then he took out a small handful of little new metal washers and gave a few to each of the children.  He said that these represented all the good things in life.  Then he talked about how in this mortal existence the good and the bad are all mixed up together and sometimes the good is hard to find amidst all the bad stuff around us.  He had the children drop their metal washers in the sand or dirt and stirred them slightly and pushed them underneath so that they couldn't see them.
        He talked about how it might be hard for them to find the good things and how they might get dirty while searching through all the dirt.  But he had a way that would make it easier to find and attract the good things in life.  He told about the Holy Ghost and how he helped us do this.  He pulled out a magnet and likened it to the Holy Ghost and had one of the children hold it over the sand and move it about ----all the little metal washers came right up and attached to the magnet.
    Then he talked to the parents a minute about how we want to surround our children with the good things of life, close at hand, and all around them---------good music, good friends, literature, movies, scriptures, FHE, etc.
    He then gave each of the children a magnet to keep--to remind them to seek good things and that the Holy Ghost would help them to do this.

It was short, effective, and interesting to the children and involved them, so they paid close attention.