I remember reading a book a few years ago, maybe around 2015, where some sort of virus has infected everyone who was older than maybe 16 years old, turning them into zombies. That means the children were trying to survive by scavenging the city. The main group of the book was situated in a supermarket.
Later they tried to run away from the supermarket because they some of them were supposedly killed in a scavenging mission. The mission involved a public swimming pool. I think one of them survived for some reason and was running around alone for a while facing the adults, trying to get back to the supermarket. One of them chose to stay in the supermarket and was slowly going insane until the adults finally managed to break through the defenses the kids originally put up to secure the place.
The main group was trying to cross the city and was running through a little park at some point where they were attacked in the night. They also had a few skirmishes on the strees
Later they arrived at a palace of sorts where another group was situated. They were trying to show off how much food they had when the new group arrived, but they were just as poor as the first group. There were some power struggles between the groups and some wanted to go further.
The one who ran around alone found the empty supermarket at one point and decided to go further. In the underground he met some adults who were not turned into zombies by the virus. They were still trying to eat him, though they intended on cooking him first. When he ran away they got to the surface where they suddenly turned into zombies.
Random things I still remember:
- the defenses were pretty elaborate thinking that a couple of frightened kids in a post-apocalyptic world were supposed to have created them
- the main group had a dog - I think it was the sister of the guy who ran around alone who was caring for the dog
I am sure that this is the first book of a series. Can you help me remember which one?