Stages of child language acquisition

It is thought that language development may begin before birth, in the womb.  Some evidence to support this theory comes from the following studies

DeCasper and Spence (1986): Babies sucked on their dummies more when they were being read a story, by their mother, that had also been read during the last six months of their time in the womb.

Mehler et al (1988): Four-day-old French babies sucked on their dummies more when they heard French as opposed to English or Italian.

Fitzpatrick (2002): The heart rate of a newborn baby slowed when it heard its mothers voice

This stage occurs at 6 - 8 weeks. 

Babies begin making a small range of sounds, getting used to moving their lips and tongue.

This begins with vowels (/u/ and /a/), which they then link to produce extended vowel combinations.

They then begin using velar consonants (/k/ and /g/, made using the back parts of the tongue)

These sounds carry no meaning, it is simply vocal play

The babbling stage begins at around 6 months old. 

Babied produce repeated consonant/vowel sounds, like 'mamama' or 'gagaga'. (Reduplicated or canonical babbling)

Sometimes these sounds are not repeated 'gagiga'. This is called variegated babbling.

Deaf babies who have been exposed to sign language will babble with their hands.  This suggests babbling is innate. 

Some people argue that babbling is a continuation of experimentation, and some argue it is the beginning of speech:

Petitto and Holowka (2002): Noted that most babbling came from the right side of the mouth, which is controlled by the left hemisphere of the brain, which is the side responsible for speech production.

Phonemes first increase then contract.