This is discussed about 10 threads down from yours....here is what I posted, so I hope it helps.
Search on google and you'll find tons of suggestions on child safety in crowded places. I have seen some interesting products, such as:
1. Who's Shoes (whosshoesid). It is a velcro enclosed label that goes on the child's shoes. It has the following fields, which are hidden by the velcro cover.
* Child's Name
* Parent's Name
* Emergency Phone
* Physician's Name
* Phone Number
* Medical Conditions
* DOB
2. Angel Alert (Target)
This is a two piece electronic device. If the child strays more than xx feet from you, it goes off.
Designed to set off the alarm in closer distances when crowds are denser, and further distances when child and adult are within sight of one another.
o Range is approximately 30 feet, depending on conditions
o Child's transmitter includes a panic button
o Can be attached with neck cords or clips
o Includes 2 replaceable, long-life lithium cell batteries with 200+ hours of operating life.
o Adult unit is 2.5 inches x 1.5 inches x .5 inches
o Child unit is 1.5 inches x 1.5 inches x .5 inches
o Unit can also be used to protect Alzheimer's patients, pets or purses, luggage or backpacks.
3. Child Locator (Target)
This is really cool, but I wish they combined the features of the above item with it. It is a pink or brown bear that goes on the child's shoelaces/straps and if the child gets lost, you press your transmitter button and the bear yells, "Mommy, I'm over here."