Possible Clues:

• Don't tell!
• Tell no-one the solution to 'Palindromic relation'
• Tell nobody the answer to 'Palindromic relation'
• Say nothing in article probing parental intelligence
• Say nothing!
• "For your ears only" ... and a hint to first words of 17-, 27- and 48-Across
• Keep this to ourselves
• What do you call your mother? Keep it to yourself!
• Complete silence is demanded
• 'Don't tell!'