Firstly, in general I made a slightly different choice from the author of the FA in that from an early age I would actively and very obviously lie to my child sometimes. I wanted them to be able to tell when someone was lieing and know that people lie all the time and you need to not just trust people but check things and think for yourself. I started with very exaggerated and obvious lies and moved on to more subtle things. I made it pretty obvious it was a game. Think of Calvin's dad explaning science in "Calvin and Hobbes".
Seperately I think it's really important to be serious and honest to your child when they ask you serious and honest questions. So for example, they came to me one day and said "Tell me the truth, does Santa Claus exist?" and I said "Do you really want me to tell you?" and they said "yes". So I told the truth.
You need to be really straightforward with children from a really young age including about topics you think they may not understand yet. For example I've seen in some of the sibling comments people talking about difficulties introducing children to topics around sex etc. I _guarantee_ if you take your child to a farm or zoo or even just a walk in the park and see dogs "playing" these topics will come up. You have to pick an angle that works for you but be straightforward.
Me: I'm off to go slay some dragons.
Them: you don't slay dragons
Me: what do I do?
Them: you code computers to catch bad guys... Black marketers or something.
This was age 7 or so. At the time I worked on algorithms to detect rogue traders in financial markets.
My mom and stepdad always told my sister that Santa is not real but that we pretend he is as a fun tradition. She was fine, and this didn’t seem to hamper her enjoyment of Christmas at all. I plan to do the same with my kids, if I ever have any.
Last year I humorously told my 7yo kid that Santa Claus died of COVID. Already before COVID though, we had the Christmas tradition of watching Futurama's "Xmas Story" episode, pretending that Santa has been replaced by a murderous robot who kills people during Christmas day.
It's all a matter of perspective. In our case, we've replaced mythology with humor and subversion - I prefer the latter to the former, and the kid fully embraced it (making the Futurama episode our tradition is their idea) :)
