The "Map" Tia carries in the original—a star chart—could be reimagined. Perhaps it’s not a map to a star system, but a frequency—a signal left for them by their "parents." The climax isn't them flying a spaceship away, but activating a dormant beacon that calls for extraction, forcing the military to stand down as a massive shadow covers the mountain.
We are currently living in the golden age of "stranger things" and super-powered fugitives. It is time to revisit Witch Mountain, not as a nostalgic romp, but as a gritty, sci-fi thriller. Here is the pitch for the remake we actually need: escape from witch mountain remake