Write a script appropriate for children, ages 3 to 14. The script should avoid adult content, but should incorporate "adult" themes. Don't condescend to your audience.
Cast the movie with actors. Casting can be a major factor in how successful your movie will be. Some famous movie directors, like Billy Wilder, cast "against type," putting actors in roles they do not traditionally play. This is an interesting way to challenge actors.
Film the movie. The production phase of the movie is stressful, requiring you to balance the demands of many different people. Remain open-minded to different directions the story can go, to make this phase inspiring and interesting.
Edit the movie with standard movie-editing software, like Movie Maker or Final Cut Pro. In the editing room, the movie really comes together.
Test screen the movie with family and friends. Take their advice, especially the advice of your family that watches a lot of children's movies, about how the edited film could be improved with further revisions. Make final edits to the movie, based on their advice.