The development of language involves two distinct processes: receptive i.e. what the child hears and understands and expressive i.e. what the child speaks to express himself.
The first indication that the child will be able to speak in future comes at the age of 2 months, when the baby coos. Cooing is some gurgling “throaty” sounds made by the baby in response to a person “talking” to the baby.
At 3 months, the child listens to music and seemingly enjoys it (an example of receptive speech) while at the same time he starts to say “aah, gnah” (expressive speech).
At 6 months, the baby starts to babble. This is monosyllabic e.g. “ma” or “pa” or “da” etc. At 8-10 months the babbling becomes more complex with multiple syllables (“ba-da-ma”) and the inflections mimic the native mother tongue. But whatever he speaks is not a true language or a meaningful word, which comes at the age of 1 year (see below). That’s why it is called babbling.
At 7 months, the child follows one step command with gesture while at 10 months he follows one step spoken command without gesture (e.g. Give it to me; Go there etc.).
The first real word that is meaningful and pertains consistently to a specific object or person makes its appearance at the age of 1 year. This is the ideal age for verbal language acquisition, mainly through picture books. With a picture book as a common, shared focus of attention, the parent and the child can engage in pointing and labelling of pictures, with elaboration and feedback by the parents. This way the vocabulary of the child increase as he now knows names of specific things e.g. flower, moon, sun, star etc.
Receptive language precedes the development of expressive language (because the child has first to receive and understand words before being able to express it). Thus by the time that the first meaningful word makes its appearance, he already is following and responding appropriately to several simple commands like “no”; “give me” etc.
At 15 months, the child is able to point out to main body parts. At this time, he has a limited vocabulary of his own of 4-6 words that he can utter meaningfully. The way the child speaks at this age is “broken” and “fast” as if his mind wants to convey a lot of things, but his tongue is not able to keep pace with it because he doesn’t have the required vocabulary at his command. So this speech is aptly termed as “jargon speech.” At 18 months, the child has progressed a bit. His vocabulary consists of 10-15 words and he is also able to name pictures (if so trained).
Between 18-24 months, there is a dramatic development in his linguistic capabilities. The main reason for this is that now a child points towards an object, not with the purpose of having it, but rather to know its name. The child points towards an object and asks the adult “what is that?” i.e. tell me its name. The realisation that words can stand for things is a very important phase in the language development, so much so that his vocabulary increases dramatically from 10 words at the age of 18 months to 100 words at the age of 2 years. At 2 years comes another important linguistic milestone and that is putting words together to form a sentence. The child can usually put 3 words together (subject, verb, object) at this age to form a sentence.
At this stage, the child can follow 2 step commands. Now he can carry out 2 separate commands joined by “and” e.g. “Give me the book and then go out to play.”