Child Chaser

If you don't want to embed an RFID tag in your kids neck, you could also get the ionKids tracking system:

Wristags transmit a signal to the Base Unit from up to 350 feet when outdoors and up to 200 feet indoors. Because it uses a point-to-point wireless communication system, the ionKids Wristag does not rely on cell towers or satellites to locate your child-so cloud cover or a building's roof will not prevent you from finding your loved ones.

Additionally, every few seconds, ionTechnology™ simultaneously changes the transmission frequency, Wristag ID and corresponding information in the Base Unit, significantly reducing the chances that a third party can scan or monitor a child's Wristag. In addition, each communication between an individual Wristag and its Base Unit will be transmitted on a different frequency, making it possible for multiple Wristags to be used in the same close environment without transmission interference. -Ion-Kids