@mathias I was solving exactly that problem recently. I think it boils down to 1) the language in which the little reader consumes; and 2) availability of good content at various local marketplaces. In my case, browsing my local Amazon porfolio quickly showed that it's a non-starter for my little reader.

Another consideration for me was the format in which the local/national library lends e-books. Again, Amazon was quickly a no-go.