You are right, Otto's World. The Hobbit was a children's story, intended to be read to the little ones by the fireside when the day's activities were done. Tolkien had no idea what was coming after that. Even when he started LOTR, he intended it to be another children's story, just a sequel to The Hobbit. I suppose he just got carried away, and ended up with a huge volume which, eventually, was split into three parts.
Taking this to heart is important to the movie. It will be difficult to encapsulate this and at the same time meld the five together, making it a "five part series."
