Going back to gr gr gr grandparents it's usually about 7 children.
My great nan however was one of 13 (i have only been able to find 9 mind). I know that my great great gandad was one of...7, i think, and in 1881, his next door neighbour was his uncle and his uncles family, which was i think 8 kids?
My nan was only one of 5, but her father died young. My moms father (who died when she was only 2) was one of 7 but only a few survived.
My dad (who comes from Ireland) was one of 7. His sister has had 13 children, and between them she has over 60 grandchildren, and 6 great grandchildren!
Me - I am one of 10 children, number 8 actually. The eldest born in 1967, the youngest born in 1993.

Nowadays I know that when I tell somebody that I have 9 brothers and sister, the reaction I get is along the lines of.