I've compiled a PDF booklet that's free to download, called Using Comic Editors with Kids. It's available at my personal website, where I also keep lots of other literacy-related PDFs I have made. Using Comic Editors with Kids lists some of my favourite online comic editors and suggests ways to use them in an educational context.
The PDF is CC licensed, meaning you can download it, use it, and share it with others so long as you don't change it, don't charge for it, but give attribution to me as the creator.
What a wonderful, useful and encouraging resource you have created. Thank you for sharing it.