I have some thoughts about Jack Harkness and family, specifically in terms of how he relates to his daughter and grandson in Children of Earth.
It’s pretty clear that Jack is the closest thing Steven has to a father. Which is to say, he is not Steven’s father at all, because he comes so rarely that it’s like a treat. But better than Steven’s actual father.
Whose fault is it that Jack has such a distant relationship with Steven? In CoE Day One, when Alice makes a resentful comment about how signing checks is easy, and Jack points out that he stays away because she asked him to, that he’d come around every day if she wanted.
He’s blaming her. But it’s not entirely her fault. I mean think about it…every day? If you’ve watched either of the first two seasons of Torchwood—or, for that matter, even Children of Earth!—you would know that just isn’t doable. Jack’s job is too dangerous and too demanding.
(Or is it? Gwen pulls it off, doesn’t she? But Gwen manages just barely, and really kept her relationship with Rhys through the grace of God and his own loyalty toward her. It’s sheer stupid luck that Rhys is even still alive. Besides, Jack is the leader. A more demanding position.)
And then there’s the little fact that Jack spent the first…what, five years? Of Steven’s life prepared to leave the planet at the drop of a hat should a certain alien with two hearts show up at his doorstep. We now know that Jack didn’t just abandon the team when he left at the end of seasons two. He abandoned his daughter and grandson.
Here is how I see Jack’s relationship with Steven: He is the closest thing the boy has to a father, but he is a bad father. He comes and goes. His work comes first. We see this mirrored in Frobisher, who is busy with his job all the time and rarely gives affection to his daughters.
Someone online once pointed out that we see the name of one of Frobisher’s daughters on the door all flowery and cute, and we see Steven bleeding and shaking, and suggested maybe it means that Frobisher killed the idea of a child, and Jack killed an actual child.
(Why do we see Jack’s murder, and not Frobisher’s murders? I hadn’t thought of that, and now I’m not sure. Perhaps it's because, whether because of circumstances or personality, Jack faces the horror of his actions. Frobisher doesn’t. Or maybe it’s just because the way Frobisher kills his children is much more realistic—real adults kill real children that way—while Jack’s killing of Steven is very sci-fi.)
But that’s not true. They both killed actual children.
And they both killed the idea of children.
What did Jack lose in Children of Earth? Home. Partner. Child. In short, family. This is the thing about Torchwood’s Jack Harkness, which a lot of people don’t notice, because they’re stuck on the idea of him being this intergalactic slut, which he isn’t. In the first three seasons of Torchwood, Jack Harkness had sex with all of one person. In almost every romantic interaction he had (whether dancing, kissing, or sex), the other person took the lead. Jack is certainly always talking about past sexual encounters, but talk is cheap. Actions are more important.
The fact is, the Jack Harkness of Torchwood wants a family. He’s jealous of Gwen for Rhys, alternatively urging her to hold onto her relationship (“Don’t let it drift” “Be normal, Gwen Cooper, for me”), and getting in between Gwen and Rhys (interrupting their date in Combat, dancing with Gwen for so long at their wedding). In short, he wants Gwen to be happy, and thinks Rhys will give her that happiness, but he is intensely jealous. Not, as some people assume, because he wants Gwen (although that may be a factor)…but because Gwen has the normal life he wishes he could have. In the one with the fairies, we discover that he and Estelle promised they would never part. In Something Borrowed, we discover he was married. Both these details involve female lovers (which bothered a lot of people), but we’ve seen him willing to work at maintaining his relationship with Ianto, and when Ianto suggested the possibility that they would be together until Ianto died of old age, Jack hardly protested.
And of course in CoE Day One, Jack blames Alice for the fact that he isn’t more involved in her life, and his grandson’s life, which isn’t Alice’s fault, but isn’t entirely Jack’s fault, either.
How well did Jack and Steven know each other? Not too well, I imagine. To Steven, Jack was more the idea of a father figure than an actual father figure, a man who comes every now and then bringing money and praise. To Jack, Steven was the idea of a child, the child he never got to raise.
(Note: We also saw how Jack values family in his Grey backstory. For all its faults, the Grey story and Jack’s reaction to this event of his past emphasized just how important family is to Jack.)
Jack did not love Alice the way a father loves his daughter. Nor did he love Steven the way a father does his son, or the way a grandfather loves his grandchild. He loved them, yes, but also the idea of them. The idea of being a father, and a grandfather, of having a normal life, of having a family.
In killing Steven, he gave up on that idea.