If you liked Magic Tree House...
try these titles!
Secrets of Droon (series) by Tony Abbott
The Witch of Clatteringshaws by Joan Aiken
Time Out by Helen Cresswell
Maximum Boy (series) by Dan Greenburg
Magic Attic Club (series)
Dragon Slayers' Academy (series) by Kate McMullan
The Key to Rondo by Emily Rodda
Time Warp Trio (series) by Jon Scieszka
Pete's Disappearing Act by Jenny Tripp
The Disappearing Bike Shop by Elvira Woodruff
A Great Lakes Adventure in History and Mysteries (series) by Janie Panagopolous