Possible Clues:

• Nursery complaint
• When doubled, a guitar or horn effect
• Doubled, a psychedelic guitar effect
• ''Do __ Diddy Diddy'': 1964 hit
• Plaintive cry
• With 28-Across, sad trombone sound effect
• Cartoon baby's cry
• Infant cry
• 'Do ___ Diddy Diddy' (1964 hit)
• Cry from a nursery