Well, why not use the term "heresy" instead? "Cult" is defined either in a neutral term
cultus, meaning "worship", or in a negative term in Sociology which refers to a highly controlled religious group which various common characteristics, or another neutral term which simply refers to
"New Religious Movements".
If you are referring to a group who you believe has an incorrect belief on an essential issue, you should refer to them as a "heresy" to be more clear, "cult" already has several accepted meanings.
So you have a problem with Mormons because they don't believe the same things about Jesus as you do
God in Mormonism. But wouldn't that be the same problem a Catholic would have with a Baptist teaching their children about Jesus? They don't believe the same things about Jesus as we do, even though they do accept the Trinity (though apparently there are unitarian "Oneness Baptists" like "Oneness Pentecostals", here is
one).
It is the duty of the parents (and the godparents) to educate their children, especially about the faith. You can send your children to a school but you should know what they are teaching and they should be teaching the same thing that you would have taught them at home. If you knowingly have your children taught false ideas, it is just as though you had taught them those false ideas yourself. Many parents at my parish, and other traditional Catholic parishes, for that reason especially don't even send their children to Catholic schools -- most have become so liberal they are no longer trustworthy educators (and they still cost an arm and a leg, especially if you have several children).
So if it is unconscionable as a faithful Catholic to send your children to a Catholic school, how much more serious of a problem is it to send them to a Protestant school or even a Protestant VBS program? Isn't it just as bad as sending your children to a Mormon children's program?
Ok, so RC says her Mom and that CCD teacher are NOT part of "the church."
I am saying they are not the Church -- there's a distinction.