assign_favourite_child_effect

assign_favourite_child_effect = {
	$ACTOR$ = {
		random_relation = {
			type = favorite_child
			save_scope_as = current_favorite
		}
		send_interface_toast = {
			title = choose_favorite_interaction_notification
			left_icon = $ACTOR$
			right_icon = $RECIPIENT$
			if = {
				limit = {
					exists = scope:current_favorite
				}
				remove_relation_favorite_child = scope:current_favorite
				scope:current_favorite = {
					add_opinion = {
						target = $ACTOR$
						modifier = no_more_favorite_opinion
					}
				}
			}
			set_relation_favorite_child = { reason = favorite_child_chosen target = $RECIPIENT$ }
			$RECIPIENT$ = {
				add_opinion = {
					target = $ACTOR$
					modifier = made_favorite_opinion
				}
			}
			custom_tooltip = choose_favorite_interaction_notification.tt
		}
		hidden_effect = {
			every_close_or_extended_family_member = {
				limit = {
					NOT = { this = $RECIPIENT$ }
					OR = {
						is_child_of = $ACTOR$
						is_grandchild_of = $ACTOR$
						is_great_grandchild_of = $ACTOR$
					}
				}
				add_opinion = {
					target = $ACTOR$
					modifier = has_favorite_opinion
				}
				add_opinion = {
					target = $RECIPIENT$
					modifier = is_favorite_opinion
				}
			}
		}
	}
}

As written in game/common/scripted_effects/07_dlc_ep3_scripted_effects.txt.