rob the cradle
US /rɑb ðə ˈkreɪ.dəl/
UK /rɑb ðə ˈkreɪ.dəl/
1.
to have a romantic relationship with someone who is much younger than oneself
:
•
Some people might say he's robbing the cradle, but they seem very happy together.
•
She's always been attracted to younger men, so she's known for robbing the cradle.