Following device from Lok8u is a GPS locator device in the form of digital watch that will tell you exactly where your kid is, whenever you feel that you need to know his/her position.

Lok8u-Num8-GPS-Locator-watc

You could use mobile phone or a PC to do the tracking. The device is securely fastened to your child and cannot be removed or deactivated without your knowledge.

User could set up their own “safe zone” range. You will notice once your child step outside the safe zone.

Price:
GBP149.99 [ excluding 18 months cellular plan of GBP4.99 ~ GBP19.99/month ]

[ Source ; Product Page ]