The movie "Escape to Witch Mountain" is based on the same-titled children's book by Alexander Key. by Alexander Key was first published in 1968. But a question that is frequently asked is if the movie and/or book was based on the popular "People" stories by science fiction author Zenna Henderson.
"Escape to Witch Mountain" is not a direct adaptation of any of Zenna Henderson's short stories about "The People," but nobody can read Henderson's stories and Key's book (or see the Disney movie) without being struck by the many similarities. Henderson's "People" stories were written and published in the 1950s, 60s and 70s, some pre-dating Alexander Key's book by nearly two decades.
The central characters in "Escape to Witch Mountain" are Tia and Tony Malone, two young orphans played by Kim Richards and Ike Eisenmann. Although they appear to be human, the siblings are actually aliens who have powerful psychic abilities such as telepathy and telekinesis. They were apparently orphaned when their spaceship crashed on Earth while escaping their dying planet. All of these details except for the names match the characters and situations found in "The People" stories. The superhuman powers exhibited by the alien children are essentially identical to the abilities possessed by Zenna Henderson's "People" story aliens, including the fact that each sibling has different "specialties."
"The People," the made-for-TV adaptation of Zenna Henderson's stories, is largely disliked and forgotten. Henderson's stories are so well-written, so widely loved, and remain so unique (despite their many imitators), that it seems inevitable that they will someday be the basis for a well-made feature film. But unless one counts "Escape to Witch Mountain," that has not happened yet.