This book explains the meaning of the Mass, the significance of its parts and why it should be celebrated with such reverence. I was especially impressed with how the author portrays the sacredness of the Mass in ways that are meaningful to children. You and your children will learn about the sacred vessels and vestments, the liturgical colors and seasons, the meaning behind the various prayers and actions, etc.
A few practical notes - Because this book was written in 1932, it most precisely applies to the Tridentine Mass. However, it is an excellent study for those who attend the Novus Ordo Mass as well, and I think you'll see that the essentials remain unchanged when the Mass is properly said. My sister-in-law also assures me that the book is quite useful and applicable for those who belong to the Byzantine Rite. The book would most appropriately serve as a read-aloud, allowing for some discussion, questions and explanations along the way. It would be very suitable as an aid in preparing your child for First Communion, but is very informative for older children and adults as well.