Smiling at Faustus he said, "I think History of Magic was one of my least favorite classes when I was in school." Though having a person instead of a ghost teach it likely would have helped.
Harry then felt bad when he saw Faustus's face drop when he admitted he didn't know how to fly. If Faustus hadn't asked Severus to teach him, and comment that Severus had promised Harry would have offered. He could see though it was important to Faustus that Severus teach him.
It was a pity yhat Severus wasn't sending Faustus to the primary school though. If nothing else the interaction with the other kids might distract Faustus from how little he saw Severus. Even though he knew Severus's duties took up a lot of time, and were important, Harry could see the boy felt a bit abandoned.
"Well maybe we can do something else sometime then." Harry told him. "I'm sure you haven't explored all of Hogwarts yet and I know a few secrets to the castle that your Dad might not even know." He finished with a wink, trying to ease the tension.