That is one thing I'm curious about. I don't exactly remember how Mac seemed (somber? regretful?) when he told Reed that he and Claire never had children. But I've wondered if they didn't have children because of fertility issues, because one or both or them didn't want kids, or because they had decided to wait and ran out of time. I guess it does have a bearing on how the writers see Mac's future (as far as family and relationships) unfolding. IIRC, Mac's supposed to be in his mid-40's, so it wouldn't be unrealistic for him to still have children of his own or even adopt younger children at some point. Given the developments in this episode, however, it has crossed my mind that perhaps the writers are setting up another older, surrogate child for Mac in Ella, similar to his surrogate son Reed. Maybe they see him as already being past the stage of diapers and want to see him dealing with other types of "family" issues. Guess we'll have to see how all the family and relationship stuff plays out. They're only about halfway through the show (assuming it can make it to 9 or 10 seasons), and with that amount of time, I sort of expect to see changes to the cast as well as key relationships before we get to the end.