infantile regression
Medical/psychological term for reverting to infant-like behavior, often used for young children after a sibling's birth or during stress.
Since the new baby was born, the older child has been showing signs of infantile regression.
Infantile regression is usually temporary and often resolves naturally if you provide reassurance.
Standard kanji-kana mixed spelling.
Kana rendering of 返り; common in informal writing.
Compound of 赤ちゃん (baby) and 返り (returning), literally 'returning to babyhood'.