Try this simple outline:
Some children may insist that while they are certain they received Christ at some time in their life, they were to young to remember either the occasion or their life before Christ. In these cases, have them tell why they are glad they are a Christian.
The purpose is not for them to have a "Thank you Lord that I am not like the tax collector" attitude, but that they will be thankful to the Lord for His salvation and ready (and willing) to tell others how the Lord saved them and the difference it has made in their lives.