Often in the Proverbs, and in other places in Scripture as well, statements are made of general principles, or of ordinarily true realities.
We sometimes get in trouble if we take a verse like Proverbs 22:6 and say, “This is a guarantee that everyone who trains up a child in the way he will go can be assured that child will follow in that path.” We have the case of many godly parents in the Old Testament who saw some children not turn out well. Of course, you could say that none of us train up our children in the way we ought. None of us are the godly parents we would like to be or that we ought to be.
I think the better approach is to say that the Proverbs are talking about what is normally true and what we can ordinarily expect, not that there is never an exception to these things. I think history would say that parents who train up their children in the faith and in the church very frequently see those children being faithful and remaining faithful.