orphan; child left by the deceased
Refers to a child whose parent(s) have died. Often used in formal, literary, or news contexts. Not a casual everyday word; 孤児 (こじ) is more common for 'orphan' in general.
He lost his father in an accident and became an orphan.
There is an organization that supports children who lost their parents in the war.
He is a child left parentless by a traffic accident.
Rare, somewhat literary use for a child who has been abandoned or left behind. In modern Japanese, 捨て子 (すてご) is the usual word for an abandoned child.
In old tales, stories of abandoned children being taken in by temples often appear.
This fund supports children who lost their parents in the disaster.
The grandmother raised her orphaned grandchild.
捨て子 is the standard word for an abandoned child, whereas 遺児 in this sense is a rare, literary usage.
Compound of 遺 (い, 'leave behind') and 児 (じ, 'child'). The kanji combination directly conveys the meaning of a child left behind, either by death or abandonment.