Some of the information is Boop-Oop-a-Dooping full of SPOILERS. Boop-Oop-a-Doop!
The origin of the baby-talk singing style goes way back to the 1900s, and was quite common among a number of female performers. Most original baby-talk songs do not feature scat singing, as there is a difference between the baby-talk and the scat singing, as both styles were eventually merged into one. Irene Franklin's 1909 recording of "I've Got the Mumps" is one of the earliest baby-talk song recordings, making Irene one of the earlier baby-talk singers. Other early baby-talk singers include Nan Halperin, Peggy Bernier, Hannah Williams and the Duncan Sisters with "Baby Sister Blues" released in 1923.
When Helen Kane sued the Fleischer Studios and Paramount Pictures in court for stealing her persona and singing style, it came out that the baby-talk singing style was quite common among a galaxy of performers, thus ruling out Helen being originator of said singing style. It also came out that Helen's scat singing routine which was interpolated into her music was also not original, and that Helen had saw an African-American child performer by the name of Baby Esther Jones scat singing at the Everglades Club, the same year Helen made her debut. After Helen had saw Esther Lee Jones perform, not too long after, Helen had started to scat sing in songs. Helen Kane naturally had a high-pitch baby voice and had always sung like that too as it was quite common, she mixed the baby-talk and the scat singing together which then eventually led her to fame and fortune. Helen sung and recorded several of her hit songs in the 1920s and then became one of the most notable baby-talk singers of the 1920s, up until Betty Boop was created. Today both the baby-talk singing style and the "Boop-Oop-a-Doop" scat singing is most associated with Betty Boop.