GuardianLion has started to sell its GPS panic button device for children to carry in the USA.

GuardianLion was in the news with their concept already a couple of years ago. Now the product is apparently shipping.
This emergency gps locator has indoor tracking capability. The GuardianLion’s Amber Alarm utilizes SiRF GPS technology (site). The press of a panic button will automatically relay the kid's location information (longitude and latitude) immediately to local 911 services. Amber Alarm is currently a $350 investment with a $39.99 monthly service charge.
More details on SpatialNews and on the Gardianlion site (they need a web-site redesign badly to be taken seriously).

See also the GPS phones from Wherify.