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.