Fuzzy Mud by Louis Sachar (Kids)

They got lost.
The world got scared.
And the mud got fuzzy.

Fifth grader Tamaya Dhilwaddi and seventh grader Marshall Walsh have been walking to and from Woodridge Academy together since elementary school. But their routine is disrupted when bully Chad Hilligas challenges Marshall to a fight.

To avoid the conflict, Marshall takes a shortcut home through the off-limits woods. Tamaya, unaware of the reason for the detour, reluctantly follows. They soon get lost. And then they find trouble. Bigger trouble than anyone could ever have imagined. What they uncover might affect the future of the world.