A teacher asks her class, "How many children are there in your family, including yourself?" The mean response is 3 children. How close should this be to the cencus figure for the average number of children per family? Explain your answer.

Not really sure how to explain this correctly. I was thinking about something along the lines of...

A classroom is very small sample size compared to the census figure of the USA, meaning that it will probably be vulnerable to a lot of variance. One would say that there average children per household probably is between 1-4, so we can't be that much off.

What do you guys all think?