An introduction wouldn't be for a four year old, it would be for say ten and up, who make up a massive amount of people watching the movie. Cutting the scene is wrong not only because it is sweeping a problematic scene under the rug, it also changes a work that's already been released to the public (see George Lucas), and it ruins the movie, as the crow scene is pivotal and the story and would be confusing without it. The crows are the ones that tell Dumbo he can fly. Don't fuck with it or don't re-release it at all.