What is this film about?

I know this is a late reply, but I just found out about this movie. First of all- they made me read this book in school when I was 15 and it's terrible.

The story starts when a bunch of kids attack 9 year old Dídac because he's black, and end up throwing him into the ocean. 14 year old Alba sees everything and confronts the kids, then jumps into the water to save Dídac. While Alba and Dídac are underwater some aliens annihilate most of the human race, except for them both who were protected by the water surrounding them. Once they go back up to the surface they see what's been done and Alba starts planning to create a new world.

The book follows the next 4 years of their lives and what they learn while trying to stay alive. They start reading a lot and learn things such as medicine and flying helicopters through books (which at some point is a thing Dídac has to do), and also Alba is awaiting for when Dídac becomes sexually mature so they can start repopulating the world... And the book is not exactly explicit, but it's hella gross.

I don't know how they want to show all these things in the movie, and they've already changed a few things such as their ages, making Alba way older than Dídac... I really don't know how this is gonna work out. And I have to say I'm not thrilled this was made into a movie. i hated this book since the moment I first laid eyes on it, and after actually reading it I hated it more. I found the story quite boring and Alba is super manipulative and cold, Dídac is a little kid who is very confused by all of Alba's moods and what's going on around him. I felt bad for him a lot through my reading...