what does Papa mean when he say, "I want these children to know we tried, and what we cant do now, maybe one day they will"?

Papa wants the children to know that he took a stand for what was right, and that even if things didn't turn out right..... they'd know he tried  to make it right. He wants to instill this value in the children, he wants to know that if he fails, his children will have learned the lesson and continue the fight...... that even if his own fight is lost, that doesn't mean that they won't be able to see it through.