Jack and Annie Series (aka Magic Tree House)

Cast of Characters: Jack, Annie, Merlin, Morgan, Teddy.

All of them have to at least have Merlin or Morgan. Teddy is in some of them. There's no actual bad guys. They might find some bad guys in each book, but there's no actual bad guys. In every book they go on a mission in a magical tree house. They travel through time on each mission.

These are the ones I have read:

Book #1, DINOSAURS BEFORE DARK
Book #2, THE KNIGHT AT DAWN
Book #3, MUMMIES IN THE MORNING
Book #4, PIRATES PAST NOON
Book #5, NIGHT OF THE NINJAS (Oooh, Night of the Ninjas was great)
Book #6, AFTERNOON ON THE AMAZON
Book #7, SUNSET OF THE SABERTOOTH
Book #8, MIDNIGHT ON THE MOON (This was a good one too)
Book #10, GHOST TOWN AT SUNDOWN
Book #11, LIONS AT LUNCHTIME
Book #12, POLAR BEARS PAST BEDTIME
Book #13, VACATION UNDER THE VOLCANO
Book #16, HOUR OF THE OLYMPICS
Book #18, BUFFALO BEFORE BREAKFAST
Book #19, TIGERS AT TWILIGHT
Book #20, DINGOES AT DINNERTIME
Book #21, CIVIL WAR ON SUNDAY
Book #22, REVOLUTIONARY WAR ON WEDNESDAY
Book #23, TWISTER ON TUESDAY
Book #24, EARTHQUAKE IN THE EARLY MORNING
Book #26, GOOD MORNING GORILLAS
Book #27, THANKSGIVING ON THURSDAY
Book #29, CHRISTMAS IN CAMELOT
Book #30, HAUNTED CASTLE ON HALLOW'S EVE
Book #31, SUMMER OF THE SEA SERPENT (I just read this today)
Book #33, CARNIVAL AT CANDLELIGHT
Book #37, DRAGON OF THE RED DAWN
Book #38, MONDAY WITH A MAD GENIUS
Book #42, A GOOD NIGHT FOR GHOSTS (I just read this today)
Book #43, LEPRECHAUN IN LATE WINTER (My teacher read this to me)