Codea is a really nice lua development environment for the iPad and can also be used to create App Store apps (though you need to use Xcode to build the app bundle). There are quite a few others but I think Codea is noteworthy.
Honestly the whoLe ‘I wish I could code on my iPad’ thing and complaining kids can’t learn to code on them, has been tired for a very, very long time. Many of these dev environments came out more than 10 years ago now. Being able to develop in swift and publish to the App Store directly for the device for free was announced at WWDC and released last year, but people still keep moaning about it. Pay attention people!