Cognitive Connie
Understanding language development in toddlerhood
Toddlerhood (roughly 12 to 36 months) is the period in which language most visibly erupts. The child who produced no recognisable words at 10 months will, by 36 months, have a productive vocabulary of several hundred to over a thousand words, combine words into sentences, and be an active conversational partner. No other developmental window shows comparable linguistic growth in so short a time.
Key figures
Roger Brown
1925–1997Conducted the landmark longitudinal study of three children (Adam, Eve, and Sarah) that established the canonical stages of early language acquisition. Described mean length of utterance (MLU) as a better index of language development than chronological age, and documented the order in which grammatical morphemes are acquired.
Susan Carey
b. 1942Coined the term "fast mapping" and documented the naming insight — the child's discovery that words are conventional, stable labels for categories. Her work showed that a single exposure can be sufficient to attach a new word to a new concept.
Ellen Markman
b. 1946Proposed the lexical constraints framework — including whole-object assumption, taxonomic assumption, and mutual exclusivity — as cognitive biases that help children solve the reference problem in word learning.
Key concepts
Vocabulary Explosion
The rapid acceleration in word learning that typically occurs between 18 and 24 months, during which children may add 10 or more new words per week. Associated with the emergence of the "naming insight" — the understanding that words are not context-specific signals but stable, conventional labels for categories of things.
Fast Mapping
The ability to acquire the approximate meaning of a new word after only one or two exposures, without the repeated pairings required by associative learning models. Susan Carey demonstrated that preschoolers fast-map novel colour terms in a single brief exposure. Underlies the speed of vocabulary growth from toddlerhood onward.
Mutual Exclusivity Constraint
The assumption that each object has only one name, so a novel label is most likely to refer to an object not yet named. Helps children map novel words to novel referents even in ambiguous referential environments. One of several lexical constraints proposed to explain how children narrow down the logically vast space of possible word meanings.
Telegraphic Speech
Two- to three-word utterances that omit grammatical function words and morphological inflections while retaining content words that carry the core semantic content. Characteristic of children between approximately 18 and 30 months. Named by analogy to the economical style of telegrams. Despite surface simplicity, telegraphic speech typically preserves the canonical word order of the ambient language.
Overextension and Underextension
Common word-use errors in toddlerhood. Overextension: applying a word too broadly, using "dog" for all four-legged animals. Underextension: applying a word too narrowly, using "cup" only for one particular cup. Reflect the child's active but imperfect hypothesis-testing about the scope of word meanings.
Child-Directed Speech Expansion
Adult caretakers spontaneously expand children's telegraphic utterances into grammatically complete forms — when the child says "daddy go," the parent replies "yes, daddy is going." Expansions provide corrective feedback in a conversational context and are associated with faster language development.
Test your knowledge
Sources
Last reviewed July 2025- 1.
Brown R. (1973). A First Language: The Early Stages. Harvard University Press.
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The foundational longitudinal study documenting early language acquisition stages.
- 2.
Carey S. (1978). The child as word learner. In M. Halle, J. Bresnan, & G. Miller (Eds.), Linguistic Theory and Psychological Reality. MIT Press.
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Original proposal of fast mapping and the "naming insight."
- 3.
Markman E.M. (1989). Categorization and Naming in Children. MIT Press.
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Systematic account of lexical constraints in early word learning.