Jumanji by Chris Van Allsburg, 1981.

Judy and Peter, a brother and sister, are left home alone while their parents go to an opera. In spite of their parents’ warning not to make a mess because they’ll be bringing guests by later, the kids scatter all of their toys around while playing. Then, the kids go to the park to play for awhile, and they find a board game labeled Jumanji with a note that the game is free to anyone who wants to play it. Judy and Peter decide to give the game a try and take it home.

Jumanji turns out to be a kind of race game. Players are supposed to make their way down a path through a jungle, facing all kinds of dangers, until someone reaches the golden city of Jumanji. The instructions warn them that once a game has begun, it will not be over until one of the players reaches Jumanji.

At first, Peter thinks that the game is boring and easy, but it soon becomes apparent that things that happen in the board game are starting to happen in real life when a live lion suddenly appears after an encounter with one on the game board.  Peter is scared and wants to stop playing, but Judy reminds him that they can’t stop because the game won’t end until one of them reaches the end of the path on the game board. Until the game ends, they’re stuck with the lion and anything else that happens to appear because of the game. They have no choice but to keep playing, facing each danger as wild animals rampage through their house.

Chris Van Allsburg books always have amazing illustrations, and the pictures in this book are especially good!  At the end of the book, the children see two other children find the game, which leads to the sequel, Zathura.

There is a movie version of this book, but the movie differs greatly from the original story. In the movie, the two kids were friends, not brother and sister, and the boy ends up trapped in the game for a period of years until, finally, a new set of kids starts playing and helps the original players to finish their game.  When their game ends, the original children are returned to their own time, and no one but them knows that they were ever gone.  Things turn out better for the future children as well because the older players make things better for everyone in their own time.  There were no players stuck in the game in the original book, and everything takes place during a single day.

The book is currently available online through Internet Archive.