Could it be "Innocence", a ST:Voyager episode?
Tuvok crash-lands on a moon along with Ensign Bennet. Bennet does not survive and his remains are stored in a containment field in the damaged shuttle. Tuvok discovers three children, Tressa, Elani and Corin. They tell him the craft they were on also crashed, killing the adults. They convince him other members of their race, the Drayans, mean to do them harm. Tuvok helps the children elude a search party. Later, when the danger passes, they behave as children normally would, getting into things they should not and asking incessant questions as Tuvok tries to contact his ship.
The leader of the Drayans, Alcia, contacts Voyager to say they have found the shuttle and the crewman should be removed as soon as possible. The planet is sacred to the Drayans and their presence desecrates it.
Tuvok's efforts fail as two of the children, Elani and Corin, vanish in the middle of the night. Captain Janeway and Paris take a shuttle down to the surface while being pursued by other Drayans, who do not wish the shuttle to sully the sacredness of the moon. Soon, a confrontation occurs between the aliens and the Voyager crew. The crew believe the aliens mean to harm the last child, until it is finally explained that they were not children at all, but actually confused Drayans at the end of their life; their species ages in reverse.
Tressa recalls the truth about her circumstances. With Alcia's permission, Tuvok promises to stay with Tressa to the end.