Children and fools say things without thinking; they say what they think or know when grown-ups might not think it was polite or wise to do so. A proverb. "Uncle Willie is too fat," said little Agnes. "Children and fools speak the truth," said her father.
CHILDREN AND FOOLS SPEAK THE TRUTH
Meaning of CHILDREN AND FOOLS SPEAK THE TRUTH in English
American idioms English vocabulary. Английский словарь американских идиом. 2012