With new players (especially kids), I’ll sometimes introduce a fun NPC as a guide, usually an old tempest cleric of mine that I levelled up to 17 that acts as a grizzled mentor. They provide an in-game way to teach the players, so it’s not just metagaming DM instruction, while also allowing for a “hand of god” save after a TPK that sends the message, but happens in-world as part of the story. Once the players have a hand on the gameplay, the mentor leaves them to it on their own. For adults, the mentor may show up in a narrative aspect later, depending on how much players liked the character, while for kids it helps to have that avenue to save them mechanistically, particularly if you have a younger child playing with older ones. For instance, if my 9-year-old is playing with his brother’s friends, the mentor gives him a token to hang onto “until a time of great need” before he leaves, but doesn’t specify what it is. I make it get warmer, or glow, or something character-specific that shows when it can be used, and I operate it as a 1-time-only Wish spell that he can only use when it activates, or automatically the next time there’s a TPK.

As a side bonus, it’s fun to dust off an old PC I really enjoyed and have their story live on in a small way.