Every parent of a small child should have the FBI's Child ID app. It can be used to store photos and vital information, such as height and weight, so that info is readily available if a child goes missing. The app can be used to call 911 and the National Center for Missing and Exploited Children, as well as to email the child's description to the police and other authorities. There's also preventative advice on how to keep kids safe. Available for Android and iPhone.