I've seen that suggested on the DISboards before as a tip. There are also some sort of tattoos you can have printed up with your phone number that you put on your kid, in case the kid gets lost the phone number is easy for a CM to find if it's on the kid. What I do is get ID tags for my kids at the pet store and put them on a simple, cheap sturdy necklace chain. They love their "necklaces" and think it's hilarious that they match the cat. I like that they are removable but easy to find and read in case they get lost. The kids have been instructed to go to a CM working behind a register (since you can buy look-a-like nametags, I don't tell them to find any CM) or another mom with kids, and tell them that they are lost and show their necklaces. Many times kids will panic and forget their phone number or give the home number instead of the parents cell phone number, or little ones might not know the number or their parents first names. It's a great idea to have the number on them somewhere. I've resorted to writing the number on my girls' arms if we forget the necklaces and are in a crowded public place.
I got lost at the mall when I was a kid and it was terrifying. This was in the days before cell phones, but if it hadn't been you better believe I'd have been happy to write a phone number on my ankle with a Sharpie, just to avoid that feeling of being scared.