Magic Tree House

#1 Dinosaurs Before Dark by Mary Pope Osborne, 1992.

Eight-year-old Jack is walking home with his seven-year-old sister, Annie, when Annie spots a tree house in the woods that they’ve never seen before.  In spite of Jack’s warnings, Annie climbs up into the tree house and yells down that there are a bunch of books in there.  Jack loves books, so he also climbs up into the tree house to see what she’s found. 

There are books in the tree house about all sorts of interesting times and places.  When Jack starts looking at a book about dinosaurs, he wishes that he could see one himself.  Suddenly, the tree house takes the kids back in time to a land filled with dinosaurs.  The two of them have some hair-raising adventures as they try to figure out how to get back home, getting some help from a friendly Pteranodon when they need to escape from a Tyrannosaurus Rex. 

The kids figure out that the tree house will take them anywhere they want as long as they look at a picture of the place in one of the books and wish to go there.  There is a book about Pennsylvania in the tree house with a picture of their home town in it, so all they need to do is to look at it and wish they were there in order to go home. 

While they are still in the land of the dinosaurs, Jack finds a gold amulet with the letter M on it.  He thinks it belongs to whoever owns the tree house, so he picks it up and brings it back with them, although by the end of the book, the kids still don’t know who it really belongs to. The ownership of the tree house is something that they eventually figure out through their adventures with it. (See book #4 in the series for the answer.)