I have a six year old son with this same fascination. Sometimes I'll walk into my home office and find some mailer with a QR code sitting there waiting for me. His inquisitive mind just has to know what the phone will do with the code.

You can pick up barcode battlers on ebay for cheap. Although they're probably antiques now.

I've got some somewhere, but I don't think they did QR codes and they certainly didn't launch a link - that's what she enjoys. No idea why, but I'm not going to discourage her from anything that gets her interested in technology. We're going to get a t-shirt printed for her with a QR code saying "If found, please ring [phone number]".

First thought: this might be a neat Android game Second thought: this has already been implemented

And..

https://play.google.com/store/apps/details?id=com.fawepark.a...

(by the way, this displays in an awful Spanish for me, because of my default language)