I don't know if your magicband has that info somewhere, but I don't think magicbands are scanned routinely to find out parents info. A good tip I've learned is take a picture of your kid everyday so you can describe what they're wearing in an emergency. We never did anything special, but once the kiddos were old enough to do so(around 4), we had them memorize one parent's cell phone number. I have seen people that write phone numbers right on the magicband with sharpie or do dog id tags in the laces of kids shoes. One caveat with the phone number thing, we lost our at the time 11 year DD at the aquarium at Epcot. I think we actually wandered away from her, but I digress. Anyway, she quickly found a CM and asked to call her parents because she was lost. It took them like 10 minutes to find a cell phone for her to use to call us, so the phone idea isn't as great as it sounds. By that time, we had found her. And this was a non-panicked older kid so I don't know how well that would go down with a younger panicky kid.