Telling the children that they had always lived in the country.
In Plato's Republic, there is a short bit in which this was recommended that if a people are brought somewhere to found a city, they should all tell their descendants that they had sprung out of the ground itself. That way, those children would be loyal to the city and the land, not being tied to the origins of their ancestors who came from elsewhere. There is a word that is a synonym of "indigenous": "autochthonous". The etymology of this word is from the Greek roots "auto" for "self" and "kthon" for "earth", implying that a people came from the ground itself.