I think that was very kind of you to give them your input and time and that you were respectful but frank with them.
I think your suggestion to the man to ask the elders about child abusers within the congregation is an excellent one. It's a benchmark too. I would also suggest that he ask them to let him know if any future abusers join. That way, if anything ever happens to any of his children, he has some ammo with the authorities. It also puts responsibility on the elders.