I wrote in detail about Storybird in Create Story with Storybird and used it to respond to my own prompt in Creative Prompt - Start with Illustrations. In a nutshell, at Storybird, kids can use pictures from adult illustrators, adding their own writing to match, and create a digital book.
I've embedded a sample Storybird I made below.
Princess Sophie on Storybird
Toon Doo Books
I wrote in detail about Toon Doo Books in Making a Book at Toon Doo. In a nutshell, at Toon Doo kids can compile a book of their single cartoons, made from Toon Doo's art work and templates, with children's own words added to speech bubbles.
I've embedded a sample Toon Doo book I made below.
I wrote about Storyjumper in Create a Story with StoryJumper. In a nutshell, kids use props, scenes etc from the site, and add text to make a digital book. They can also upload photos. (I notice you can now order single printed books, and pay for them, but US and Canada orders only.) I can't find an embed code, but you might be able to check out the book I made online.
If you haven't had a chance to create digital stories with your kids, I urge you to explore one or all of the options above. Combining a literacy activity with the creative process is a wonderful way to develop skills that children will use for life.