Mama. Dada. Dog. Baba. Gama. Papa. Ball. More. Cat. Few things are more exciting than the first words of a baby. Babies will usually utter their first words between 10 and 15 months of life. Although it takes nearly a year for a child to speak, infants spend this year preparing to utter their first words.
Within the first few months of life, babies begin the process of developing language. At birth, an infant’s vocal cords are not sufficiently developed to make sounds like speech. This doesn’t mean that babies can’t communicate though! Crying is a very effective communicative tool for a newborn and as everybody who has spent the night staring at a baby knows they make a lot of bizarre noises. Nevertheless, within 6-8 weeks of birth the vocal cords are sufficiently developed for a baby to begin to make “ooooo” and “aaahh” sounds. This form of speech is called cooing, but I like to think of it as baby-watching-fireworks-noises. Around the same time as cooing emerges, babies also gain enough motor control over their mouth to try out other noises: raspberries, grunting, squealing. Babies don’t only practice these different vocalizations, they also practice volume. We affectionately called one of my children “the pterodactyl” after the loud, excited, squeaking noise that erupted when we got home from work.
The next developmental step in infant language production is babbling. Babbling is putting together 2 sounds, a consonant and a vowel (e.g., “ma,” “ba,” “pa,” and “da”), and putting them in a chain (“mamamama”). Regardless of what a babies native language is, infants babble with a few common consonant sounds, like “m,” “b,” and “d.”  As babbling continues, babies will begin to take on the sounds, intonations, and patterns of their native language (even if the sound itself doesn’t occur in their native language). That is, babbling begins to take on the sound characteristics of a child’s native language over time. In a classic study from the 80s, adults could pretty accurately identify an 8-month-old as French or Arabic/Cantonese just by listening to their babbling. 
Early vocalizations like cooing and babbling are especially interesting in congenitally deaf infants. This is because they give us information about the nature and nurture (the biological and environmental) features of language development. Until 5 or 6 months of age, congenitally deaf infants produce vocalizations similar to those of hearing babies. This tells us that auditory environmental stimulation is not required for cooing. Remember that babbling begins around 5/6 months of age – in deaf infants, babbling occurs later in development and is limited compared to hearing babies.  This tells us that environmental experience of hearing language is important for babbling. Indeed, deaf babies who are exposed to sign language during the first months of life do babble at the same rate and frequency as hearing babies – they just babble with their hands.  Deaf babies use small motor features of spoken words and repeat them with their hands – almost like stuttering a word. This also tells us that there is an important feature of babbling – of looking at small features of words – that allow children to ultimately make meaningful, longer words, within their native language.
Once a child begins to make vocalizations, one of the most important things a parent or caregiver can do is to engage in a “conversation” with their baby. These conversations are incredibly important for future communication skills of the infant. They go something like this:
Baby: “Oooooo ooo oooo gurgle gurgle.”
Adult: “I see! Yes, that is a block.”
Baby: “gagaga baBAbaBA ma..ma…ma…. [massive spit up] SQUEEEEAAAALLLL.”
Adult: “Oh, my! Poor baby! It feels so much better that you threw up all over me doesn’t it? So much better.”
This ridiculous talking that we engage in with babies is actually critical for four reasons. First, it teaches babies how conversations work! You make a noise, and then I make a noise. I listen while you talk; you listen while I talk. Turn taking is taught during these early periods of speaking and listening that adults are modeling. In fact, children are more likely to learn a word from these turn-taking interactions than they do if a caregiver just labels the object outside of a turn-taking conversation. 
Second, babies will imitate the sounds of the conversational partner, using more high pitch vocalizations with mom and lower ones with dad.  This tells us babies are learning about pitch and volume differences from these conversations.
A third important feature of these chats is the shared attention between the child and adult. This is called joint attention or intersubjectivity – and basically means that two people are paying attention to the same thing. Joint attention is a key feature of communication. Conversations don’t work unless you can agree on a topic. Pointing, which emerges around 12 months of age, is a method of children to communicate with somebody about something. It basically means, “Look at this!” – let’s communicate about it.
Fourth, during these interactions adults usually name objects for the infant, which is how an infant learns new words. For instance, if the baby is playing with a rattle, adults rarely talk about the weather. Instead, they say, “rattle! That is a rattle! Shake, shake shake! The rattle makes a shaking noise!” This style of interaction helps a child learn that the word “rattle” is associated with this object. Now, whether that word is the object itself, the noise it makes, the waving motion of one’s arms - that is something that a baby has to figure out. This is called the problem of reference. Young children frequently make errors in assigning words but eventually, with more experience, they will correct these errors. For instance, some children call dogs “woofs.” This is actually a pretty logical mistake. If an infant sees a dog and somebody says, “Doggie! Woof!” – it is a logical assumption that that the fluffy, four-legged animal may very well be a woof and not a dog.[a] In one of my favorite examples of this, a friend of mine’s child called women’s breasts “milks” for years.
Before children are able to produce their own words, we know that they are able to understand words. By about 6 months of age, infants will turn their head toward the appropriate person when hearing “mommy” or “daddy.”  In one study, researchers used a looking-paradigm to see how many words 6-month-old babies understood. In looking-paradigm studies, researchers present two images, side by side, and measure which image an infant looks at. Looking illustrates that the infant associated that word with an object. When presented with common types of food and body parts, infants looked at the correct image more often than would be expected by chance – suggesting that some babies have an understanding of the word-object association as young as 6 months. This is important because this is almost 6 months before an infant will speak a first word! As some have noted, infants are little scientists in the crib, listening, learning, and comprehending long before we realize it.
Finally, between 10 and 15 months of age, babies produce their first word. What counts as this? Turns out, developmental psychologists love to fight about this one. Two friends of mine – who are both experts in child language development – once got into a screaming match at happy hour over whether or not a child’s utterance counted as a first word or not. While it was quite awkward for the non-scientists at the table, I thought it was hilarious. And for the record, I thought it should be counted as a first word. That’s because I like the definition that a “first word” is any specific utterance consistently used to refer to something or to express something. Even if it isn’t close to the correct word, to me, the key feature is the consistent use of the word with the object or action. This would mean that you might count the word “nana” if it is consistently applied to “banana” or “ouchie” if it is consistently applied to a stove. One of the best first words every belonged to my nephew, who at 12 months called all trash a “yucky” – obviously because every time he picked up trash his parents said, “Yucky!”
In the U.S., babies learn nouns first and evidence suggests moms label more nouns than other types of words (like verbs).  This is not true in other cultures however; In Korea, mother use more verbs than nouns,  which explains why infants in Korea learn nouns and verbs at the same rate, unlike English-speaking babies who learn more nouns than verbs.  While there are cultural differences in the language learning of children, there is also substantial similarity. For instance, in English, Mandarin, and Cantonese, “Daddy,” “Mommy,” “Bye,” “Hi,” and “Uh-Oh” are all in the top ten lists of first words.
So what does it all mean? First, infants are basically geniuses. They begin learning language and communication from the moment they are born – and as soon as their vocal cords allow them – they are ready to start participating. One of the most important things parents and caregivers can do with their infant is to interact with them. The more words a child hears the more rapid his or her language development will be and the more varied his or her vocabulary. Moreover, remember that infants are not just learning words. They are learning the social-communicative skills that will help them to be a good conversationalist all throughout their lives. Talk to infants as much as you can. Talk to them like they are listening – because they are.
[a] One interesting thing that children do when they learn a language is they overextend a word. For example, children will call all 4 legged animals “dogs” or all women “mama” – it takes a while for kids to figure out that each animal (or grown-up) has a different name. This issue is discussed in the language section in early childhood.
 Boysson-Bardies, B. D. (1999).
 de Boysson-Bardies, B., Sagart, L., & Durand, C. (1984).
 Oller, D. K., & Eilers, R. E. (1988).
 Petitto, L. A., & Marentette, P. F. (1991).
 Goldstein, M. H., Schwade, J., Briesch, J., & Syal, S. (2010).
 De Boysson-Bardies, 1999.
 Tincoff, R., & Jusczyk, P. W. (1999).
 Fernald, A., & Morikawa, H. (1993).
 Choi, S. (2000).
 Choi, S., & Gopnik, A. (1995).