Labelling the children

So we've been thinking about how to "label" the children while in Germany. Assuming one of them will get separated from us how should we best ensure their safety and our ability to reconnect? We have to admit we are vulnerable in this area. We've lost a kid in Walmart (twice) and on our last "big city" vacation we lost one in the Field Museum in Chicago. Poor parenting I know, but true. My usual Sharpie on the underarm method for Disney seems unrealistic for a three month time period. We found some ID bracelets that we can order from Amazon.de and that seems the easiest solution, we fill in our cell phone number and they wear them when we are out and about. These are designed for toddlers, but given our limited German I need something for all the kids. Its really scary to lose a kid, I can't imagine doing it in a foreign country. Yes, we did consider GPS. I wonder what they think of the "kid leash" in Europe??