QOW for FI

This question comes from reader Edelle, who emailed us to ask:
At my parish, we are looking into starting a Sunday school, a weekly faith formation program for young kids in our parish. I once attended a mass with a similar program. The children were taken to a classroom sometime during mass for activities related to the Sunday Gospel. We're not too sure of the mechanics of this program though--what age group, what part of mass they leave, when they come back. If your parish has a program like this, could you explain the specifics of how such a program would work?

Please share your answers and experiences in the comment box below.