rob the cradle

Idioms  

1. Have a romantic or sexual relationship with someone much younger than oneself, as in The old editor was notorious for robbing the cradle, always trying to date some young reporter. [Colloquial; first half of 1900s]

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Example Sentences

I ain't like some men that rob the cradle for farm hands and puts little lads building roads when they are so small they have to be weighted down with stones in their pockets to keep them from blowin' away.

From Project Gutenberg