noun
lucky person; fortunate person
Refers to someone who has achieved success or happiness through good luck rather than effort. Often used in a slightly literary or formal context.
彼はまさに幸運児だ。
He is truly a lucky person.
彼女は幸運児として生まれた。
She was born a fortunate person.
ラッキー is a casual loanword meaning 'lucky', used as an adjective or exclamation, whereas 幸運児 is a more formal noun for a lucky person.
Compound of 幸運 (good luck) and 児 (child/person). The exact historical derivation is uncertain, but the word is conventionally associated with a person favored by fortune.