Can you explain a theory of pragmatic development in Child Language Acquisition?

Michael Halliday (1975) suggests that we need language because we are forced to interact with other people and with our environment. As we get older and language becomes more complex, so does the social sub-text it carries; however for young children, most utterances serve only one function at a time. The 'Halliday taxonomy' refers to the seven functions of language:

1. Instrumental: Language is used to fulfil the child's particular need e.g. "drink!" if the child is thirsty

2. Regulatory: Language is used to influence other's behaviour e.g. "mine!" so a caregiver gives something to the child

3. Interactional: Language is used to develop social relationships e.g. phatic talk such as "hi"

4. Personal: Language is used to express opinions and individual identity e.g. "I like Postman Pat"

5. Representational: Language is used to convey facts and information e.g. "Mummy gone to shop"

6. Heuristic: Language is used to learn and explore the environment e.g. "Raining!"

7. Imaginitive: Language is used to create in play e.g. "Monster coming!"