Experts advise starting conversations with children about safety about a week before a journey, taking a family photo at the start of each day, and labeling bags and clothes. (Weston Wei/The New York Times) By DANIELLE GELFAND A few months ago, my family was in the crowded Brussels Airport. Though I’d put an AirTag in my then 7-year-old daughter’s knapsack, made a bracelet with our contact information and even taught her my phone number to the tune of “Happy Birthday to You,” I had a sudden...