I don't think people can make other people "children of hell". What they CAN do is make others worst and degrade society. The Pharisees were doing just that with other people.
For example, stem cell researchers feel like they would like to use stem cells to cure diseases. Today I heard where British soccer players now want to bank their stem cells in order treat cartilage problems they'll have later in life from playing soccer. I think this is an excellent example of how we progressively degenerate society with our errors and how someone can make a person "twice the children of hell".
Here's my understanding. Eli, the priest had two sons(H & P). Eli concentrated so much on his work, thereby ignoring his sons, who turned into such bad little things, they were destroyed in O.T. King David did the same with his sons, but God just let them continue living so we could read about all the perverseness that results from the father neglecting his sons. Anyway, the whole point is, the fathers thought they were so special that the sons would just magically inherit the goodness and they needn't do a thing. And there's the double-trouble. Children must be taught. Samson is another example. His parents figured since he had special abilities from God, they could just sit back and watch the wind blow. And look at what happened in Samson's life. The sins of the father were multiplied in the sons, because the sons were not taught to do right...