We didn't seem to have different library cards for children and adults, when I was a kid. There was certainly a children's section of the library, but I was allowed to borrow books from other parts of it as well, such as Dorothy Sayer's Lord Peter Wimsey stories.

My parents had an extensive book collection, too, but not that much in the way of fiction actually. Dad had a couple of Enid Blyton books in Swedish from when he was a kid, which we did all read several times over.