One of the first post-apocalyptic books I read as a kid (maybe 5th or 6th grade). It wasn't required, but I remember having to get a certain amount of "points" based on the reading level, length, etc. of the books I selected. I tended to read sci-fi, fantasy, and post-apoc, and I still favor them all today. I have a list of these books from childhood (the ones I can remember at least) that I've been seeking out and adding to my library. A few, I even borrowed from A&M's library (children's lit section). It's great to revisit them. Other favorites include the Tripods Trilogy, the Girl Who Owned a City, Virtual Wars, Singularity, etc.
The addition of a third character and the older age of the girl definitely add a twist, but it seems to keep the overall feel. Looking forward to it.