If you only know Jumanji from the movies, you'll be very surprised by this wonderful, gentle children's book. The illustrations and typesetting are beautiful. This is suitable for reading with your young ones. I'd say they need to be old enough to understand simple board games, and of course they need to know (or be able to understand an explanation of) what a monsoon and similar things are.
The bonus audio track of Robin Williams is great. This is Williams at his most relaxed, making this almost a bedtime story.
One caution: this story is set in an era when people would hold formal cocktail parties, so it has an antique feel to it. Youngsters might not notice or care.