So you have an "older" and "younger" password. If you are the younger person (ie child) in the conversation you tell them the "younger" password, and if you are

So you have an "older" and "younger" password. If you are the younger person (ie child) in the conversation you tell them the "younger" password, and if you are the older you tell them the "older" password. or something like that. Remember this is mostly to defeat casual one-off scams.