If Marvel is supervising the marketing, then most of the final action scenes cannot be in tv spots before release. They can be used after, but not before. So if the kids only use their powers in those scenes, they won't be shown powered up in the tv spots. Marvel wants the audience to be surprised. Since they have so much attention on their tv spots, one clip in an international tv spot can lead to the whole movie being spoiled.
This is the exact opposite of what Fox used to do. They would put as much action as possible in tv spots and spoil the whole movie.