The small numbers in the margins of the catechism are references to other parts of the faith that deal with the individual paragraph's specific topic, uniting the four pillars in a synthesis and creating an organized reference book. Plus, the addition of a ribbon for every period makes it accessible to children.
This podcast episode discusses the importance of marginal reference numbers in the Catechism of the Catholic Church, as well as their usefulness for parents in teaching their children about the faith.
The speaker discusses the Chartres book, which is designed to help people better understand and appreciate Catholicism. The book comes with color-coded pillars based on different time periods and a ribbon for every period.