Magic Tree House: #7 Sunset of the Sabertooth 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!
The Ice Age is very cool…for two kids in bathing suits! Jack and Annie nearly freeze when the Magic Tree House whisks them back to the time of cave people and woolly mammoths. But nothing can stop them from having another wild adventure—not even a saber-toothed tiger!