Bizarrely, if you trasfer DRM-free ebooks directory onto your child’s Amazon Kindle, they cannot see them or read them if they are logged in under an Amazon Kids account. You can share books you bought from Amazon (on your account) with Amazon Kids accounts within your Amazon Family, which is fair, but you can’t share DRM-free ebooks with them. For that, you have to set them up with their own, independent Amazon account. That Amazon account cannot be part of your Amazon Family, so you can’t share anything with them. It is so confusing and irritating.