Parents can spend thousands to protect their kids, but one of the most important tools out there is absolutely free -- a password. No, it has nothing to do with computers: It's just the old-school trick of giving children a so-called "safe word" to use if they're in danger. As criminologist Dannah Eve explains on TikTok, "This could be used in a dangerous situation or just in simple situations where your child wants you to be the one to say no to something. If somebody is to pick your child up from school that's not you or your partner, give that individual this code word so that your child knows that that person is trusted by mommy and daddy."