We know that children's book authors have been largely ignored by other programs and we don't intend to make the same mistake. That said, it's not currently the perfect solution for picture books, though we are working on it!
There are some workarounds. You can create a book completely out of full page images, if you had all the artwork and the text was embedded into the graphics. Atticus does allow for full bleed, but not currently as a spread. To create a spread, you'll have to have 2 separate images, but that can also be done. We have an Image Sizing reference page here: https://www.atticus.io/image-sizing-for-print-and-ebooks/
We also have a quick demo tutorial showing you how this can be done: https://www.youtube.com/watch?v=7XHo8NLNg8I&t=24s
Atticus is also integrated with BookBrush, so you can use their program to create pre-sized images to use within Atticus, and there is a feature to create a single spread that they automatically separate into two perfectly sized images to insert into Atticus.