Many child safety advocates have argued that any child ID should not be visible or easily accessible to others; the fear of child abduction has spawned these fears.
I have not been able to find out information about "Tracker" but I will give you three superb resources that can provide you with countless resources (including ID systems) and information about this topic:
World Net Fundraising 1-800-244-7615
SAFE-T-CHILD, Inc. 1-512-288-2882
National Center for Missing and Exploited Children 1-800-THE-LOST
I'm sure these resources will give you all the information you need.