Sing "Before I Take the Sacrament" (CS, p. 73).
Show a picture of the Last Supper and explain that just before His Crucifixion, Jesus gave His Apostles the sacrament so that they would have a way to always remember Him and His sacrifice and so that they could have His Spirit to be with them.
The sacrament is such an important ordinance that during a solemn assembly in the temple, the First Presidency and the Quorum of the Twelve Apostles administer the sacrament to the congregation. In our wards, the Aaronic Priesthood is responsible for administering the sacrament.
In advance, invite a deacon, a teacher, and a priest (counsel with the bishop/branch president) to come to Primary to give short talks about their duties relative to the sacrament and how they came to understand the importance of it. (See Elder Jeffrey R. Holland’s general conference talk, "This Do in Remembrance of Me" [Ensign, Nov. 1995, pp. 67–69]. You might share excerpts of it with the Aaronic Priesthood as you ask their help.) Ask them to be prepared to answer some questions about their duties.
Ask the children to listen for the three things we promise, or witness, when we take the sacrament that we will do (take upon us the name of Jesus Christ, always remember Him, keep His commandments) while the priest reads. Have the priest read from Moro. 4:3 the prayer on the bread. Discuss their responses.
Ask: "What does the Lord promise us?" Have the priest again read, "that they may always have his Spirit to be with them."
Share your own testimony of the importance of having the Spirit with you and the blessing that it is to take the sacrament.
Thank the young men for helping and for their parts in administering the sacrament.
Sing "Help Us, O God, to Understand" (CS, p. 73).
For younger children: Choose pictures of the life of Christ and talk about Him and how He loves little children. Sing "To Think about Jesus" (CS, p. 71). Tell the children that we think about Jesus during the sacrament.
Sing the song again and show the pictures while you are singing.
Practice thinking about Jesus by showing the pictures again while everyone is as reverent and quiet as can be.
Tell the children that it is a joy to see them growing up and learning to control their thoughts and actions, that learning to think about Jesus during the sacrament will bless their lives.