Children's Acquisition of Language. 

Phonological Development. 

Vowel sounds, since they are made without contact between different parts of the mouth, appear effectively from the first moment that the child draws breath and cries. Consonantal sounds, made by the interaction of two different parts of the mouth, start to appear with the basic biological noises that the baby makes in its first weeks, although they are probably involuntary. Thus, recognisable sounds will appear during the prelinguistic stages, although some sounds may not be fully under the child's control for some time yet.
At the age of about eight weeks the child will start to produce cooing sounds, which consist of a consonant-like sound produced towards the back of the mouth, followed by a vowel-like sound. At the vocal play stage (from about twenty weeks) the sounds become steadier and of longer duration. Nasal sounds[i] and fricatives[ii] appear.
At six months or so babbling will commence. This sounds a bit like language, but doesn't seem to make sense: it seems to be part of biological maturation, and not determined by environmental factors. It sounds even more like language when the melodic utterances stage commences about twelve weeks after the onset of babbling, and intonation becomes a significant feature.
By the time the child utters its first recognisable word, a lot of its phonological capability will be in place, but some sounds will not be mastered for several years. We can make some general statements about children's tendencies in uttering consonantal sounds, viz. front consonants such as b, t, m are used before back consonants such as k, g; plosives[iii] such as b before fricatives such as z and oral sounds such as d before nasal ones such as ng.  Typically, we might expect that by the age of two years the child will have acquired p, b, t, d, m, n, w; by two and a half, k, g, h; by three, f, s, l, y; by three and a half sh, ch; by four dz (as in judge); and by six z (as in pleasure).
Consonantal sounds in the stages prior to full mastery are more likely to be pronounced correctly at the beginning of the word than in the middle or at the end. Where there is a problem with the pronunciation of a particular sound, it is likely to be replaced by another sound.

 The following trends can be found in many children:

§         Stops may replace fricatives, e.g. brudder for brother

§         Alveolars may replace velars, e.g. playin for playing

§         Consonantal clusters may be avoided, e.g. hwee for three

§         Consonantal sounds at the end of words may be omitted, e.g. ca for cat

§         Unstressed syllables may be dropped, e.g. cause for because

§         The r sound (and sometimes l) may be replaced by w, e.g. wun for run.

© CD Selwyn-Jones 2003