Babies begin developing language at birth. By 12 months, they may have mastered a few words and usually understand far more. Speech development is extremely variable, but language skills develop in many subtle ways.

• At 1 month of age, infants turn to a soft voice, especially a parent's voice. Around 3 to 6 weeks of age, babies use different cries to communicate, such as a shrill cry for pain or a whimpering cry for fatigue.
• At 2 months of age, babies begin to “talk” by cooing, making “ih” and “uh” sounds. They may show some variation in tone and will coo back. Babies respond to familiar voices and watch the speaking mouth.
• Around 5 months of age, infants begin to express themselves by babbling. They repeat consonant sounds like “ba,” “ma,” or “ga” to get attention and express feeling. Some babies may recognize their own name.
• Between 6 and 9 months of age, babies repeat sounds they hear. Babbling continues, but they may also mimic the rhythm of the way others talk to them. By 9 months, babies can recognize the word "no" and wave "bye-bye" when prompted. It is during this time that babies begin to make the link between sound and meaning and are able to follow simple commands like "give me the doll."
• At 12 months of age, babies may understand and use "mama" and "dada" correctly when referring to their parents. Babies may recognize their own names or look at family members or pets when you talk about them. Typically, babies this age understand some familiar words, although they are still guessing about many other words and their meanings. They may jabber an incomprehensible stream of sounds with tone and inflection that sound like conversation.