Use an airline baggage tag as temporary ID
Here's how Gillian helps make sure her son is findable in crowded airports:
We've traveled a lot with our 4 and a half year old son and I'm always worried that he will get lost in the airport. On one trip he became fascinated by the little baggage tags at the counter while we were checking our bags, so I filled on out for him with his name and phone number then realized it was a great way to make a temporary ID tag for him. Now when we get to the airport we fill one out with his name and our mobile numbers and attach it to the back belt loop of his pants. It's out of the way so he doesn't tear it off but still visible should he get lost.
Personalized rubber bracelets as wearable identification
'Tattoo' your kid with your cell phone number
Sharpie your cell phone number on your kid's belly