SOLVED. MG-YA adventure about a boy who shrinks [s]

[Molly]

I'll give as much detail as I can remember but it has been a while since I read this. I read this book sometime probably in the mid-2000s. I'd say the book was aimed at MG and maybe YA, based on the age of the main character (who I think was in his early teens).

This is what I remember of a story: A boy finds himself in a jungle all alone. He finds a group of people (I think the same age as him) living in a tree. Eventually he figures out he has been shrunk and he decides to travel back to his home to try and get un-shrunk. A couple people from the tree go with him. One of the scenes I remember is them trying to cross the road to his house and the main character is overwhelmed by the smell of fumes from the cars, and him and his friends almost get run over a ton of times. Eventually he makes it back to his house where the big version of him and his sister are returning home (from school?). He touches fingers with his big-self and becomes big again.

It's the first in a series but I only read the first book.

Hopefully this is enough info, it's about all I can remember! Thanks!

EDIT: The cover, at least in Australia, had two layers. The first had a circle cut out of it through which you could see the main character who was featured in full on the second layer.

[Tab]

The Dark Ground maybe?

Here is a portion of the Booklist review:
BookList:
Gr. 6-8. While on a plane with his parents and sister, Robert Doherty blacks out, and when he awakes, he is cold, naked, aching, scratched, and alone in a dark, damp forest. What happens next is a combination of survival and coming-of-age as Robert tries to obtain food, clothes, shelter, and water. When someone leaves a blanket and food outside his burrow, he keeps watch and eventually connects with a small band of people--small in more ways than one. As it turns out, Robert’s rescuers, and Robert himself, are shorter than a blade of grass. Although the others desperately try not to think about the past, Robert is determined to remember and to return home.

[Molly]

Yes that's it! Thank you so much!