I appreciate their concern. We should be “salt and light” in the world. However, I think a closer look at the passage and the context will help us see who that mission is actually directed to. In the gospels where this is written, salt and light are meant to be Christian influences in a dark and sinful world. It is only logical that in order to be a Christian influence in the culture, you must be a Christian. So, first you must ask yourself if your child is a born again believer.
Second, we must ask, “In what way can my child be salt and light?” — “Is my primary or secondary level child able to have an effect for Christ in the school?” — “Can he effectively explain the gospel?” — “Can he disciple a believer?” — “Can he defend his faith when under attack?” — “Can he withstand the constant bombardment of non-Christian teaching, non-Christian thoughts, and non-Christian acquaintances?”
In the vast majority of cases the answer would be no, and if the answer is no, then your child can’t be “salt and light.” In a rare case the answer may be yes, but you are obviously putting your child at great risk. Sending a child into an environment that is anti-Christian in philosophy is subjecting the mind of your child to daily teaching that is determined to replace God in every subject and every area of life.
How many young Christians can even discern that they are being fed worldly ways of thought? You might ask why the vast majority are not able to be “salt and light?” It is really quite simple—they are just (kids), and kids are not the ones that Jesus told to be salt and light—it is adults. It is the same reason that children do not lead Bible studies, become pastors, or go to foreign countries as missionaries.
They are not mature enough emotionally or spiritually, and for that matter, can’t even provide their own physical needs. They are at a time in their life when their primary function is to be a good student, not someone who teaches or disciples others. They are still being trained for adulthood and are still in the care and direction of their parents.
That goes full circle back to the Christian parents’ responsibility. We are called to protect and nurture our children in the ways of Christ so they can grow up to be world changers for Christ—no longer little saplings, but instead, strong oaks for the Lord!