Night of the Purple Moon (The Toucan Trilogy, Book 1) by Scott Cramer
Dust from a passing comet turns the moon purple, but also carries a lethal pathogen that attacks the hormones produced during puberty. Within hours, adults are dead. Thirteen-year-old Abby must help her brother Jordan and baby sister Toucan survive in the new world.
Battling against hunger and violent gangs, Abby is helpless against the biggest threat of all: the time bomb that is her adolescence.