To add an artist bio to your book, from a desktop (not currently available on mobile) in the editor, click on the first image in your book.
If you do not see the sidebar come up, try clicking on the image again.
In the right sidebar, click create a page. This will NOT remove or replace the image you are currently on, it will just add an additional page to the book.
In the layout selection in the right sidebar, select artist bio or one of the other intro options to create your bio or intro page.
If you want to upload a photo of your child that is not already in the book, in the right sidebar click My Gallery. Then click to upload your photo. Once your photo has been uploaded, drag and drop it onto the page. In the right sidebar, you can customize the color, font & text.
Once you are happy with the page you've created, simply click add to book in the top right corner to add it to your book!
Keep in mind that if you chose a colored backdrop for your page, it will not print full bleed. Always make sure to preview book to see how the printed page will actually look!