Children's phones have been present for a few years, but now all four main wireless carriers in Japan have all started marketing keitai for children. Docomo has their Kid's Keitai, KDDI has their Junior Keitai, Softbank has their Kodomobile, and Willcom has their Papipo.
These phones come with parent-oriented features like limited web access to kid-safe sites, white lists for numbers calls can be received from or made to, location maps to track you child's position and panic buttons that sound alarms, call a pre-set number and start taking pictures and collecting GPS information to automatically send to the parents phone by email. Wireless Watch Japan has a nice article about mobile phones for kids in Japan. There's also a video interview with AU Designing Studio's Manager Natsuko Kimura where she demonstrates some of the features of KDDI's keitai's for kids.
Here's a commercial for the KDDI Junior Keitai campaign
