Severus let an expression of mild amusement grow on his face even though his instinct was to take Faustus and get far away from Narcissa. "Indeed. I believe I shall have to ensure that I have retired from teaching before this new generation gets to Hogwarts."
He decided to let her make of that what she wanted. He'd actually enjoyed teaching Draco but some of the other terrors had been highly annoying. And he already knew there was another Weasley in the world.
A smile, proud smile grew on his face and he glanced down at Faustus who was giving him a small worried look. He lightly squeezed the boy's shoulder in reassurance. Faustus was smart enough to pick up some of the undercurrents even though he likely wouldn't understand them.
"Yes, I do," he said calmly then he decided on a bit of misdirection. He suspected anything he told Narcissa would end up in Lucius' ear and then be told to Rodolphus. Therefore he needed to design his answer for those ears. "Given my role for the Order, it has not been safe until now for Faustus to live anywhere but with his mother."
He gave a small polite smile and was tempted to make some comment about being a grandmother but two things stopped him - one was Faustus whom he would do a great deal more than simply be polite to protect and the second was Draco who would surely prefer it if he and Narcissa weren't openly brawling in front of the children.