Yes, I'm cheating here because I'm not finding an English compilation of City of Children the second installment that Dark Horse translated.
Should we call this a quest story? Possibly, as Sarah will not give up her search for her three children. She believes that they are alive, and if anything it is implied that they must be alive for her sake. Where she found Tunnel Town was run by the Mother Earth (ME) faction, City of Children is maintained by Epoch.
The majority of citizens and soldiers are children, hence the name.
The theme might be what war does to even children, but a stronger story point is what happened to Sarah's infant and later Sarah herself, as much of this installment includes flashbacks. No spoilers to be given out (not at this stage, anyway).
If anything Sarah becomes more real and human in this installment.