Eighteen-month olds might have anywhere from five to 40 words in their vocabulary. That can include nouns like “ball” or “cup,” as well as words like “hi” and “please.” They might be able to mimic quite a few words they hear in conversation, as well. Every child is different, though, and the normal language-development range varies widely, so always check in with your pediatrician if you have concerns about your child’s development.