Komodo is available as a Windows App, Mac App and to use in-browser. Click "Choose Your App" to choose the option for your computer.
Yes you can. We think big screens are best for young learners. So if you have an iPhone 6 or 7, or better still an iPad, it will be easier to for your child to use than the earlier generation iPhones 4 & 5.
Yes, they're free to download and install, however you'll need to register for a free trial in order to log in.