Okay, a lot of people have pointed out the parallels between Jack and the Doctor: both are would-be heroes, immortal, and doomed to lose everyone they love. In Children of Earth, with the introduction of Jack’s daughter Alice Carter and her son, Steven, another similarity was established: both are, or were, grandfathers.
(For any TW and NuWho fans who don’t know: the Doctor’s first Companion was his teen-aged granddaughter, who attended school in 1960s London under the name Susan Foreman. They eventually landed in a Dalek-conquered London in the year 2164, where Susan fell in love with a human freedom fighter. The Doctor left her there, promising, "One day, I shall come back...Until then, there must be no regrets, no tears, no anxieties. Just go forward in all your beliefs and prove to me that I am not mistaken in mine." She appeared in the twentieth anniversary special The Five Doctors, apparently coming from and returning to 22nd-century Earth. To the best of my knowledge Susan has never been mentioned in NuWho, and presumably she died in the Time War.)
A question: why did the writers give Jack a grandchild? They could just have easily made Steven Jack’s son, and Alice an ex-lover instead of Jack’s daughter. I believe that RTD & Co. intended Steven’s death to be another twist of the knife for viewers familiar with Classic Who — once again, Jack falls short in comparison to the Doctor. While the Doctor cut his ties to Susan in the hope that she would live a full life, marry, and rebuild a shattered Earth, the fact that Jack stayed in touch with Alice and Steven is why they were taken into government custody, and why Steven was on hand when Jack realized that he had to sacrifice one child to save the millions who were being collected for the 456. Susan lived to see adulthood; Steven, still a child, died horribly, at his grandfather’s hands.
Note: x-posted to torch_wood.
ETA: In a comment to my post on torch_wood, eandh99 pointed out a striking similarity between CoE and the 1979 Quartermass serial. Coincidence? Hommage to another Verity Lambert production? Rip-off?