I'm gonna start this off Larry-style:
I BELIEVE THE CHILDREN ARE OUR FUTURE:
I don't think Sun and Jin are out of the game yet. I don't think it's easy to say that anyone is. They made a point of discussing their daughter earlier in the episode, and I'll be damned if the children don't play into this in a larger way by the time all is said and done!
From the beginning, we've had the children stolen from the flight. We've had Walt and his uncanny connections (the bird and the glass door, the polar bear comic, "taller ghost walt"), we've had the fortune teller's reaction to Claire's pregnancy, we've had the problems conceiving on the island and Juliette brought in as a fertility specialist, a statue of Tawaret - the Egyptian Goddess of fertility who watches over pregnant women - standing guard over the island before eventually being destroyed, we've had Aaron born on the island, Ben brought to the island as a child, Miles born on the island, and now at least one mystery child running around freaking out Smoke-Locke. Sun and Jin have a daughter in one timeline, Jack has a son in the other.
These things simply cannot be dropped. Again, they made a point of reminding us of the Kwon child in the last episode. Do you think they would abandon her so easily? Or simply erase Jack's son from existence? There are still versions of Sun and Jin out there, as there are versions of Charlie, Locke, Shannon, Boone, the 815 pilot, and everyone else we've Lost. Not only do they exist, but they are gradually being integrated between the two timelines. No one's out of the game officially just yet, and somehow the children will factor into this. Perhaps in the end everyone will be given a choice of their life, their purpose. Would Jack choose the island over his son? Could the childless Sun and Jin be given the chance to raise their otherworld daughter?