The Gerer Rebbe, the Imrei Emes, was once present at a shiur given by his father, the Sfas Emes. At some point during the shiur, when the talmidim were having difficulty grasping his deep concepts, the Sfas Emes turned to his son and asked, "Do you, too, not understand?" The Imrei Emes just shrugged his shoulders as if to say that he too was puzzled. However, as soon as his father left the room, he stood up and gave the talmidim a clear explanation of what had just been taught.
His father, standing outside, heard what was going on, and later inquired, "When I asked if you had understood, why didn't you say Yes?" The Imrei Emes replied, "Were father to ask whether I had understood, I would have answered accordingly, but when it was assumed that I did not understand, I could not contradict father's words by affirming the opposite..."
Reb Yissachar Dov of Belz was sitting with his family at the Seder table, and his four-year-old son Aharon, who was later to become a great Rebbe, curiously eyed all of his movements, some of which were strange and unusual. The Rebbe had made these movements especially to arouse his son to ask Ma Nishtana, but the young Aharon did not ask. Attempting to help him open up, his father prodded, "You seem very curious about all the strange things I'm doing, so why don't you ask even one question?"
"Your actions really do surprise me," his son replied, "but I didn't ask, because on father you don't ask any questions."
When Reb Avraham of Sochatchov was a child, he was taught by his father, Reb Zev Nachum of Biala. One day, the father posed a complicated question in Gemara, but his gifted son came up with a solution right away. Reb Zev refuted his son's reply, and smacked him lightly on the cheek, saying, "You'll have to get out of the habit of answering quickly without thinking deeply beforehand."
Years later, when his father was old and ailing, Reb Avraham went to visit him. Reb Zev brought up what had occurred decades earlier, and admitted that after researching their discussion, he had discovered that his son's explanation had in fact been correct, but he had not told him so, lest this make him conceited. Now, however, he wanted to ask forgiveness.
Reb Avraham confessed that he had known he was right, but he had not mentioned anything because of the mitzva of kibbud av.
Halacha teaches that even in a situation in which a son must speak up, he should do so respectfully. For example: If he sees his parents doing something wrong he should not tell them so outright, but instead he should ask them, as if he is himself unsure about it. They will understand the hint and not be embarrassed.