впасть в ребячество

• ВПАДАТЬ/ВПАСТЬ В ДЕТСТВО (в МЛАДЕНЧЕСТВО)

[VP; subj: human]

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1. to lose one's mental faculties because of old age:

- X впадает в детство{{}}≈ X is entering (falling into) his second childhood;

- X is getting (becoming) senile;

- X is in his dotage.

     ♦ "Не все в старости впадают в детство", - сказала Тёща... (Зиновьев 2). "Not all old people fall into a second childhood," observed my mother-in-law (2a).

2. Also: ВПАДАТЬ/ВПАСТЬ В РЕБЯЧЕСТВО to act, think etc as a child would:

- X впадает в детство{{}}≈ X behaves like a (little) child (kid);

- [in limited contexts] X is experiencing (enjoying etc) his second childhood;

- X is being childish.