Answer:
I have a few things in my mind which I have often longed to say for the instruction of the young; for it is in one’s tender early years that such things will best take root and be most enduring and most valuable.
Step-by-step explanation:
In this sentence, Twain explains why he believes that youth is a good time to learn moral values. After explaining that he has some things to say to children, he argues that it is during these years that such moral knowledge starts to take root in a person. He also believes that the things we learn during these years are the most enduring and most valuable in our future lives.