Halliday, M.A.K. (2004). Three Aspects of Children's Language Development: Learning Language, Learning through Language, Learning about Language. In J.J. Webster (ed.), The Language of Early Childhood: M.A.K. Halliday, pp 308-326, Ch. 14. New York: Continuum - ISBN - 0826488250
Learning Language (p. 308) - a child starts learning language from the moment he is born. In fact, the baby has started learning language before he was born ... from birth onwards, he is actively involved in communication, exchanging signals with the other human begins around him.
Learning through Language (p. 317) - refers to language in the construction of reality: how we use language to build up a picture of the world in which we live ... the part played by language in shaping and transmitting the world view of each and every human culture
Learning about Language (p. 322)- coming to understand the nature and functions of language itself
First published in Yetta M. Goodman, Myna M. Hausser and Dorothy S. Strickland (eds.) Oral and Written Langauge Development: Impact on Schools. International Reading Association & National Council of Teachers of English: Proceedings from the 1979 and 1980 IMPACT Conferences. pp.7-19.
Also see Pauline Gibbon's Scaffolding Language, Scaffolding Learning (2002), Ch. 7, pp. 118-139