Sherlock is about to counter Watson's assertions when Ted asks about Archie.

"He's the son of my protegee Kitty," he tells him. "Watson and I are his godparents."

"He's adorable," Joan tells Ted. "You'll have to meet him and Kitty someday."

Sherlock considers reminding Watson of the fact that Kitty is cagey around strange men, but decides not to. Ted is not like other men, and Sherlock could see Kitty feeling comfortable with him, even if she might be overcome by the man's enthusiasm at first.