I use VitalID bracelets. They velcro and have a slip-in card - allows me to write info I want on there, including allergies, etc. My kids are typically fine with them. When my daughter was little, I'd put hers around her ankle.
If you have MB, the CMs can scan them and get your info. Our last trip, my kids knew our phone numbers, so with that and the MBs, they didn't wear the ID bracelets much.