In reality, the 90 percent of teachers to whom you refer need to learn what the Mass is before attempting to teach Sunday school. Better to have no Sunday school than to have the blind leading the blind!
We are not Protestants for whom Sunday school is sometimes considered to be equal to the main worship service. Mass is like nothing else. Nothing on the face of the earth can equal what happens on the altar. Any sacrifices we make are miniscule compared to the sacrifice of our Lord’s very body and blood. I don’t mean to berate anyone here, but to miss the supreme importance of the Mass is to not understand Catholicism at all.
The Catechism reminds us:
The command of Jesus to repeat his actions and words “until he comes” does not only ask us to remember Jesus and what he did. It is directed at the liturgical celebration, by the apostles and their successors, of the memorial of Christ, of his life, of his death, of his resurrection, and of his intercession in the presence of the Father (CCC 1341).
Further, if the children aren’t preschoolers, they should be at Mass as well.