As Betty Birner from the Linguistic Society of America suggests, children acquire the language automatically and without formal teaching. Parents don't teach their children the language in the same manner teachers do. What they do however, by interacting with the child, is allow him to listen to the words and intonation and connect them to a certain meaning. Therefore, children who have not listened to a single word cannot possibly acquire the language.
Children don't create a language of their own, they just reproduce what they hear from other people. Even the meaningless words they use when referring to objects are actually mispronunciations of correct words they have heard from others. Imitation also allows students to use irregular forms of words, even before they learn about them at school. For example, children learn to say "teeth" instead of "tooths," when they hear their parents use the word.
Children learn new words every day. However, their parents -- or other people talking to them -- don't explain the meaning of each word, as dictionaries do. Instead, children use the context to decode an unfamiliar word. They ultimately come up with a definition -- however accurate -- that helps them include the word in sentences of their own. This process has been organized in the Latent Semantic Analysis (LSA) theory.
Blocking occurs when an irregular form blocks the application of a general rule. In the English language, irregular forms are ubiquitous in verbs, such as eat-ate and nouns, like foot and feet for instance. As children become aware of grammar rules, they apply it to every word, even converting what they previously referred to as "teeth" to "tooths." However, as children listen to others say "teeth" repeatedly, they get to understand the blocking principle and realize the difference between regular and irregular forms.