I would bet my left nut that when Louis B. Mayer green lighted the original he did not do so because he wanted to make a children's movie. No, he wanted to make a movie that would satisfy all audiences, both young and old, because that's where the money was. Remember, Hollywood has always been about money, and making entertainment pay. In the 21st century movies for children have become big business, 75 years ago that would have been a losing proposition. Financially, the studios needed to bring as big an audience into the theater as possible, which is why the scares in the most important of Oz films had scares to make everybody cringe, not just the little ones.
I suspect that Oz, the Great and Powerful, like the classic film, was designed to please everybody. That's what makes a film last forever. The more people it satisfies, the longer it will hang around, which is what so many people want: film immortality .