Which sounds should a child typically master by the age of 3?

By the age of 3, children typically master easier sounds that are produced using simpler articulatory movements. The sounds /p/ and /b/ are considered early developing phonemes because they are both bilabial consonants, which means they are produced using both lips. This facilitates easier production for young children as their motor skills are still developing. Additionally, these sounds are commonly found in early emerging vocabularies, making them a natural part of a child's speech development.

Conversely, sounds like /k/ and /g/ (from the first choice) require more sophisticated articulatory skills involving the back of the tongue and the soft palate. The sounds /l/ and /s/ (from the third choice) come later in development as they involve more complexity and require the precise movement of the tongue. Likewise, the sounds /ch/ and /sh/ (from the fourth choice) are more complex as they involve the coordination of the tongue and airflow, making them less likely to be mastered by age 3. Therefore, /p/ and /b/ are consistent with typical speech development milestones for that age group.