It is a tough call. Presumably, the priest lectured on this subject ( a warning), for a week or two from the pulpit on Sunday, but if parents weren't at Mass, they didn't get the message in time.
I agree that this is a difficult subject. At Mass on Sunday, the homily discussed a similar subject. Fr. made a very good comment IMO. He said "the church of God is not a temple for the righteous but a hospital for the sinner."
As a parishioner our duty is to encourage the less faithful to come to Mass, set an example of being a good Christian, and to keep the door open so that everyone can hear the word of God. God will do the rest.
God gave us free will so that we could come to him williingly. This is only shutting the doors on "sinners" by refusing their children religious instruction and possibly sacraments. I fear for the future of the church, if it becomes ok to withhold religious education to children because their parents are not good Catholics.