Language development in children follows predictable stages that can be observed across different ages. When observing children over a week, one would notice distinct patterns in how they acquire and use words.

At one year of age, children typically enter the one-word stage. Their first words usually contain one syllable, such as 'ma' or 'da'. These single words are called holophrases as they convey whole sentences or phrases. During observation, one would note that the child understands more words than they can speak and may learn a few new words during the week.

By two years of age, children enter the two-word stage (around 18-20 months). This stage exemplifies telegraphic speech, which contains mostly nouns and verbs, similar to telegrams. The child would be observed combining two words meaningfully, and the vocabulary count would increase significantly compared to the one-year-old.

Close to three years of age (beyond two-and-a-half years), children's language development gets focused on rules of the language. They begin to understand and apply grammatical structures. During observation, one would notice more complex sentence formations and a rapid increase in vocabulary.

Overall, children proceed from almost no use of language to becoming competent language users through these predictable stages. The rate at which children acquire words and grammar is remarkable, as they create sentences they have never heard.