Shelly and I were worried about keeping track of our kids once we hit the road. We found one solution in Road IDs, the identification gear used by outdoor enthusiasts. We have one for each kid (and Shelly and I.) They have different versions, but we are using the ankle bracelet models.
I reviewed them here: http://barefootrunninguniversity.com/2011/03/05/road-id-review-keep-your-kids-safe/
For those with more travel experience, do you have other suggestions? Leave a comment!