The title comes from the final poem of the book:
When I was One,
I had just begun.
When I was Two,
I was nearly new.When I was Three
I was hardly me.
When I was Four,
I was not much more.
When I was Five, I was just alive.
But now I am Six, I'm as clever as clever,
So I think I'll be six now for ever and ever.
However, the author says in the introduction:
We have been nearly three years writing this book.
We began it when we were very young...
and now we are six.
So, of course, bits of it seem rather baby-ish to us...
So we want you to know that the name of the book doesn't mean that this is us being six all the time,
but the it is about as far as we've got at present, and we half think of stopping there.