I tell people a website is like a payment terminal. Your device is like your debit card. A password is like a PIN on the card. A Passkey is like a chip on the card.
Logging into a site with your device is like putting your card into the terminal. The site can ask for a password the way the terminal asks for a PIN, but if your device supports Passkeys, that’s like your card having a chip, and it’ll use that instead.
So think of Passkeys like using a chip card.
I dunno how well this analogy works down to the last detail but it has gotten it across to all the parents I’ve used it with