Days of Smoke and Shadow - R. A. Hargreaves - Bog

A Virus has swept through the world, killing off all the adults and leaving the kids to survive on their own.
Fourteen-year-old David has survived by staying hidden, too preoccupied with raising the baby left in his care to dream of much by way of a better future.
But a chance encounter with three amnesiac survivors, along with reports of angels and strange disappearances, forces David and the other survivors to consider the possibility that not all the adults died from the Virus and the ones who survived, may not have good intentions for the surviving children.