They never met an 18 month old like my son. At twelve months he had an over 50 word vocabulary (I wrote them down one day) At 18 months, he could talk in complete, grammatically correct sentences. You could carry on a conversation with him; ask him questions and he would answer.
You want to know what an 18 month old is capable of, meet one like that. It will blow you away. I wouldn't have believed it if I hadn't seen him (and lived with him) myself.
A youtube video conversation between a mother and a toddler child.
A Q & A about what month it is. If they know what month they were born in, how old they are and what they think about younger children. What is in a pregnant woman's belly.
“Well mom I'm only a year and a half old but clearly that professor is a liberal hack and a fool...but I repeat myself.”