Fuzzy Mud by Louis Sachar

Tamaya and Marshall have been walking to and from Woolbridge Academy ever since they were little. But one day their normal routine is disrupted by the school bully Chad Wilson challenges Marshall to a fight. To avoid getting hurt, Marshall dashes into the woods (which are off-limits), Tamaya reluctantly follows. They soon get lost, and find trouble. More trouble than they ever could've imagined!!!

I recommend this book for boys and girls aged 10+.