Which language development milestone should a typically developing 9-month-old child begin to demonstrate?

A typically developing 9-month-old child begins to demonstrate canonical babbling as a significant language development milestone. This stage is marked by the production of repetitive consonant-vowel combinations such as "ba-ba-ba" or "da-da-da." This type of babbling is essential as it lays the groundwork for later speech development and indicates an increasing ability to control vocalization and experimentation with sound.

At this age, canonical babbling is particularly important because it shows the child’s growing social engagement and exploration of vocal sounds, setting the stage for the formation of words. This milestone is a reflection of the child’s developing communication skills and indicates that they are starting to practice the rhythms and patterns associated with language.

While cooing is an earlier stage of vocalization typically observed around 2 to 3 months of age, vocatives, which involve using a person's name or title to attract attention, and differentiated cries, which are variations in crying to signal different needs, are also milestones that develop at different stages in a child's life. Therefore, canonical babbling is the correct answer as it is specifically linked to the developmental expectations for a 9-month-old.