How to be a Baby by Sally Lloyd Jones, illustrated by Sue Heap

From chapters.ca:
Take it from the narrator of this book, an all- knowing big sister: when you're a baby you don't read books. You eat them. You don't know how old you are, or even if you're a boy or a girl. And you have to keep a special plug in your mouth to stop your scream from coming out. But one day, you won't be little anymore, and then you'll be taller and smarter, and actually quite clever. Like the narrator. And you'll be able to share memories of what it was like when you were little with your incredible Big Sister.