Succeeding the 'cooing' stage, a short stage of 'vocal play' starts. The baby starts to experiment with different sounds that he/she can now make. The number of phonemes a baby can produce at this level is approximately 150. These varieties of sounds can be combined to produce any language and it is not until phonemic contraction takes place that the number of sounds is greatly reduced. The sounds produced are often longer and the number of vowel and consonant sounds is much greater than at the 'cooing' stage. Children at this age often try to manipulate the pitch of sounds to produce "growls" and "squeals" along with the loudness of sounds producing "yells". In addition, infants begin to manipulate the opening and closing of the vocal tract to produce friction and nasal murmurs such as "raspberries" and "snorts". At this stage the infant begins to master the easier sounds that appear more often in words such as /d/, /b/, /m/, /g/, /n/ and /k/. Furthermore, the infant starts to learn some of the less frequent sounds such as /f/, /s/ and /l/. This stage usually passes quickly as children become expert in the sounds associated with it extremely quickly.
Following 'vocal play' infants enter a stage that is crucial to the development of speech which is know as 'babbling'. Children add to the knowledge of 'vocal play' and start to develop sounds into strings of syllables. The syllable-like sequences are made by periodically opening and closing their jaws, lips and tongue. Between twenty-five and thirty weeks infants start to produce sounds that repeat consonant and vowel sounds such as /dadada/ and /mamama/. As time progresses these sounds become more varied and the sounds produced start to show the changing of syllables from one to the next, for instance /adu/. As the child becomes skilled in producing chains of syllables, they start to produce melodic utterances, which display discernible tones of voice. Approaching the end of this stage of development children undergo phonemic contraction. This involves the number of phonemes that can be produced being dramatically reduced. The baby will now only be able to produce the sounds relevant to their mother tongue. As this process occurs, children are able to start producing recognisable words.
At approximately ten months, children will start to produce distinguishable words. This phase of development lasts about ten months and the child's vocabulary will increase steadily at first but then increase dramatically. The first word that is produced by a child is often one that is associated with everyday occurrences, general family life or their surroundings, for example mama (mother), doggie (dog), nana (banana) or tick-tock (clock). At this point the child can only say some of the sounds needed to make up the words that they desire, so they use a word that might describe what the object does instead e.g. tick-tock. By the age of one children know approximately 100 words, this number starts to increase and by eighteen to twenty months is around 200 words. As infants only know a small number of words they use hyperextension, underextension and mismatch words. When using hyperextension children use one word to describe a series of others, for instance the hyponym 'apple' to describe all round fruit. The use of underextension only appears in some cases, children may use one word to describe a familiar thing such as 'dog' for the family dog but not associate that word with other dogs in the street. As children only have a limited vocabulary, they rarely know a word, so they use a completely different one to describe the object for example using 'doll' to describe a 'dress'. As the range of words that can be said increase, a child reaches the point of 'critical mass' which allows them to start to put words together and produce two or more words as a statement.
At eighteen months children begin to produce two-word utterances such as 'choo-choo train' and 'want juice'. As the months pass, children start to master more sounds and are able to produce more full words and groups of words. The range of vocabulary for children at eighteen months is roughly 200 words and strings of words appear. After this point, a child's vocabulary will expands at a phenomenal rate and by the age of five is around 10,000 words. This stage of development lasts approximately six months and then children progress to produce simple sentences.
As children's phonological development progresses, certain trends develop. As children start to produce sounds, some of them are mispronounced such as 'gog' instead of 'dog'. The difference in the number of vowel and consonant sounds means that children master all the vowel sounds much quicker than the consonant sounds. By the age of two and a half most children will have mastered two-thirds of all consonants and by the age of four will only have difficulties wish some consonant sounds such as 'y' in yellow which would become 'lellow'. As the various sounds are developed certain types of sounds are difficult for children to make. Consonants at the beginning of a word are usually made with relative ease but problems occur when they are at the end of a word such as in 'full'. In addition to difficulties with consonants at the end of words, vowels at the beginning of a word also provide difficulties for children of a young age. To tackle the problem of not being able to produce the right sounds children simplify words either by deletion, substitution or by reduplication to make them easier to say.
The method of simplification is two-fold; first, there is the method of deleting sounds and second the method of substituting one sound for another. When a child uses the method of deletion, they use it in three main ways. Firstly, the final consonant is often dropped for example 'Cat' becomes 'Ca' (Kæ phonetically) to make it simpler to say. Second, they might delete unstressed syllables such as 'banana' to become 'nana' (na׃na). Finally, some consonant clusters may be dropped for instance; 'little' will become 'ikle' (ik∂l). With certain words, deletion is not the preferred method and a child would use substitution instead. First, when a sound is unable to be produced, an easier one is substituted in for example, 'thumb' becomes 'fum' (fum). Some sounds such as 'th' are much harder to produce such as the 'th' in 'that' will become 'dat' (dæt). In addition to 't', the sounds 'r' for instance in 'train' and 'ch' in 'church' are extremely hard to produce initially. In addition to simplification, children also use reduplication of sounds also known as assimilation to pronounce words. With reduplication and assimilation children replace sounds in a word with another sound to make it easier to say, for example, 'cat' could become 'tat' (tæt). The methods of simplification and reduplication make the words that are need to be said easier and therefore allow children to progress at a quicker rate.
The first three years of a child's life are vital in their development of phonology and general speech. Children are extremely resourceful and use any means necessary to convey what they are feeling for example through intonation. These methods help the development of speech and their understanding of the surrounding world. Child language development does not stop when they can speak but continues to develop well into their teens. The phonological development of children is one of the fundamental building blocks that allows them to create complex sentences and engage in extended conversations that are critical later in life.