I'm trying to find a movie about children ages about 5 to teens that live alone on a planet. I think other traveler come across them & can't believe there are no adults with them. I think it's in the1960's or later. It's not a modern movie.
Sounds like this episode of the original Star Trek series: Miri (27 Oct. 1966) The Enterprise discovers a planet exactly like Earth, but the only inhabitants are children who contract a fatal disease upon entering puberty.