Kim Richards and Ike Eisenmann who play the children in this film and in its 1978 sequel Return from Witch Mountain (1978) both appear in the same scene in the 2009 remake Race to Witch Mountain (2009) where Eisenmann is "Sheriff Antony" in the bar and Richards is "Tina" the waitress. In this 1975 movie and its 1978 sequel, their names were similar, they being "Tony" and "Tia" respectively.
Tia's star case, which houses the map to Witch Mountain, had an additional purpose in the novel. In Key's novel, Tia was mute (but communicated telepathically with Tony) and carried pencils and paper in the star case to write notes to people.
The make and model of the chopper which was seen flying upside down and landed that way was a red & white Hughes 369HS helicopter with the branding of "Aristotle Bolt" which was the name of the character in the film played by Ray Milland.