I'll stick by my recommendation of javascript, because the last thing a kid would want to do is have to write their program twice so that their iPhone friends and android friends can both see it. And don't forget the hassle of tooling and publishing on the app store.
I recently came across an IRC client called The Lounge which is the single best written JavaScript GUI I've ever used. I haven't had time to pick apart the source code yet, but they built that thing with the best that web technologies have to offer. You can browse to it from any common web browser, and on mobile devices there is a button in the UI to save a link to it onto the phone's desktop as if it were a native app. It's indistinguishable from a native app and functions better than half the apps on my phone. And best of all, it's free and allows me to cross off my TODO list item for that web-based multi-platform IRC bouncer I always intended to write, and without regrets, because this is way better than what I would have created.
