Magic Tree House: #6 Afternoon on the Amazon by Mary Pope Osborne
From Random House Books for Young Readers:
The #1 bestselling chapter book series of all time celebrates 25 years with new covers and a new, easy-to-use numbering system!
Vampire bats and killer ants? That’s what Jack and Annie are about to run into when the Magic Tree House whisks them away to the Amazon River. It’s not long before they get hopelessly lost. Will they be able to find their way back to the tree house? Or are Jack and Annie stuck forever in the rain forest?