The average child masters about fifty words by the age of eighteen months. These might include words such as, milk, water, juice and apple (noun-like words). Afterwards they acquire 12 to 16 words a day. By the age of six, they master about 13 to 14 thousand words.
The most frequent words include adjective-like expressions for displeasure and rejection such as 'no'. They also include social interaction words, such as "please" and "bye".
There are three stages for learning the meaning of new words:
- Whole object assumption:
A new word refers to a whole object. For example, when an eighteen-months old child sees a sheep and his mother points at it and says the word 'sheep', the child infers that the word 'sheep' describes the whole animal and not parts of it (such as color, shape, etc.).
- Type assumption:
A new word refers to a type of thing, not just to a particular thing. For example, when the child hears the word 'sheep' he infers that it is used for the animal type and not only for that particular sheep that he saw.
- Basic level assumption:
A new word refers to objects that are alike in basic ways (appearance, behavior, etc.).
In other words, when the child hears the word "sheep" he overgeneralizes it to other animals that look like sheep by the external appearance, such as white, wooly and four-legged animal.
Contextual clues are a major factor in the child's vocabulary development.
The child uses contextual clues to draw inferences about the category and meaning of new words. By doing so, the child distinguishes between names and ordinary nouns.
For example, when an object is presented to the child with the determiner "a" (a cat, a dog, a bottle) he perceives it as an ordinary noun.
However, when the child hears a noun without the determiner, he perceives it as a name, for instance "this is Mary".
Children usually make correct meaning associations with the words that the adults say. However, sometimes they make semantic errors.
Types of semantic errors:
1. Overextension
When a child says or hears a word, they might associate what they see or hear as more generalized concept than the real meaning of the word. For example, if they say "cat", they might overextend it to other animals with same features.
2. Underextension
Underextension involves the use of lexical items in an overly restrictive fashion. In other words, the child focuses on core members of a certain category. For example: 'cat' may only refer to the family cat and no other cat, or 'dog' may refer to certain kinds of dogs that the child is exposed to.
Verb meaning: when a pre-school child hears the verb 'fill', he understands it as the action 'pour' rather than the result, which is 'make full'.
Overgeneralization
errors occur when a child extends a particular word to other referents that
share some visual or conceptual similarity. One particularly extensive summary
of early lexical development presented a large number of such errors, including
doggie (to all animals), apple (both to other round objects such
as rubber balls and round lamps, and to other fruits such as strawberries,
pears, and peaches), and moon (to a
half grapefruit, a lemon slice, a dial on a dishwasher, and a shiny leaf).
Dimensional terms
The first dimensional adjectives acquired are big and small because they belong to the size category. The size category is the most general one. Later children acquire the single dimension adjectives, such as, tall-short, long-short, high-low. Eventually they acquire the adjectives that describe the secondary dimension, such as thick-thin, wide-narrow and deep-shallow.
From birth to one year, comprehension (the language we understand) develops before production (the language we use). There is about a 5-month lag in between the two. Babies have an innate preference to listen to their mother's voice. Babies can recognize familiar words and use preverbal gestures.
Within the first 12–18 months semantic roles are expressed in one word speech including agent, object, location, possession, nonexistence and denial. Words are understood outside of routine games but the child still needs contextual support for lexical comprehension.
18–24 months Prevalent relations are expressed such as agent-action, agent-object, action-location. Also, there is a vocabulary spurt between 18–24 months, which includes fast mapping. Fast mapping is the babies' ability to learn a lot of new things quickly. The majority of the babies' new vocabulary consists of object words (nouns) and action words (verbs).
30–36 months The child is able to use and understand why question and basic spatial terms such as in, on or under.
36–42 months There is an understanding of basic color words and kinship terms. Also, the child has an understanding of the semantic relationship between adjacent and conjoined sentences, including casual and contrastive.
42–48 months When and how questions are comprehended as well as basic shape words such as circle, square and triangle.
48–60 months Knowledge of letter names and sounds emerges, as well as numbers.
By 3–5 years, children usually have difficulty using words correctly. Children experience many problems such as underextensions, taking a general word and applying it specifically (for example, 'cartoons' specifically for 'Mickey Mouse') and overextensions, taking a specific word and applying it too generally (example, 'ant' for any insect). However, children coin words to fill in for words not yet learned (for example, someone is a cooker rather than a chef because a child may not know what a chef is). Children can also understand metaphors.
From 6–10 years, children can understand meanings of words based on their definitions. They also are able to appreciate the multiple meanings of words and use words precisely through metaphors and puns. Fast mapping continues. Within these years, children are now able to acquire new information from written texts and can explain relationships between multiple meaning words. Common idioms are also understood.
(Source: https://en.wikipedia.org/wiki/Language_development#Phonological_development)
