Game concept
Favorite Child
From the game's encyclopedia
A Favorite Child is a direct descendant of the same Dynasty that a Player ruler can choose to favor. They will have a higher Opinion of you and when you die, you can choose to continue your legacy as them, instead of your heir.
Your favorite child can be any children, grandchildren, and great-grandchildren, as long as they are in your dynasty.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Favorite Child is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A Favorite Child is a direct descendant of the same Dynasty that a Player ruler can choose to favor." It is part of Interaction. Patch 1.20.1.2, from game/common/game_concepts/00_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/00_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.