Related Clues:

• "Go bye-bye," e.g.
• ''Goo-goo,'' e.g.
• It's mostly nonsensical syllables
• "Goo goo ga ga," e.g.
• Patronization technique
• Goo-gooing and gaa-gaaing
• Nonsensical syllables, maybe
• "Go bye-bye," e.g
• Sounds like childish behaviour in mini going to lecture
• Sick tabby starts to act like kitten — going ga-ga?
• Childish language
• Infantile vocalizations, and a hint to the starts of 17-, 25-, 37- and 50-Across
• "Goo-goo" and "boo-boo" (2 words)
• Infantile conversation
• Speech that's hard to follow