We have previously recommended the Amazon Fire tablet for young coders. However, the best coding game for the Fire tablet, The Foos, will no longer be available for the Fire tablet and will no longer be free. CodeSpark is developing CodeSpark Academy to build on and replace The Foos that will be available on Android, iOS, but will not be on the Amazon App Store. While there are still other coding games at the Amazon App Store such as Scratch Jr., Run Macro, and LightBot, The Foos was my personal favorite.
Sadly, this is one of the issues you run into with proprietary software. You cannot always use the software you want on the hardware you want to run it on. Sometimes, even software that already runs on the hardware you want to run it on will no longer work on the hardware. Richard Stallman would not endorse either The Foos or Amazon Fire.