The Enemy Series by Charlie Higson is a series about a disease/virus that infects all people over the age of fourteen, either turning them into zombie style cannibals, preying on children, or killing them outright. The books follow groups of children as they try to fight off the Enemy and make a new life for themselves in post apocalyptic London.
This is the order of the series so far.
There is also a short story available on Kindle: ‘Geeks Versus Zombies’, which was a World Book Day Release and is a stand alone story set in the world of The Enemy.
Charlie Higson’s website is available here.