[mcdude]

The Catholics don't call it Sunday School. It's called C.C.D. (Confraternity of Christian Doctrine) and is usually held on a weekday night and not during Mass.

The Confraternity of Christian Doctrine is commonly referred to by its abbreviation, CCD, or simply as "Catechism," and provides religious education to Catholic children attending secular schools. Similar to children’s Sunday school in Protestant churches, CCD education is provided by both members of the clergy and lay staff, although unlike Sunday school it is often held after school on weekdays. CCD attendance is considered by Vatican officials to be vital to children’s development as Catholics. These classes not only educate children about Jesus and the Catholic faith but prepare children to receive the sacraments of Penance (confession), the Eucharist (Holy Communion), and Confirmation.
Source - Wikipedia