Possible Clues:

• Cooing, maybe
• Speech that's hard to follow
• Childish language ... and a phonetic hint to 17-, 25-, 36- and 51-Across
• Patronization technique
• Goo-gooing and gaa-gaaing
• ''Goo-goo,'' e.g.
• It's mostly nonsensical syllables
• "Goo goo ga ga," e.g.
• Sick tabby starts to act like kitten — going ga-ga?
• "Go bye-bye," e.g