Final answer:
At 18 months, a child should typically have a vocabulary of around 10 to 20 words. Language development is rapid in toddlers, progressing from 50 to 200 words at 2 years old, to sentences and 1,000 words by age 3.
Step-by-step explanation:
A child at 18 months should have a vocabulary that typically ranges from 10 to 20 words. At this stage, children are in the "one word" phase of language development, where their utterances are limited but often carry significant meaning, such as expressing a desire or identifying an object. By 2 years old, vocabulary usually expands to between 50 and 200 words, with further growth leading to up to 1,000 words and sentence formation by the age of 3. It is during the toddler years that children experience sizable increases in vocabulary, sometimes referred to as the "vocabulary spurt."