When I was a kid, I loved conspiracy theories. When you're growing up you learn just how inconsistent the world is, and it's very comforting to have an explanation other than "well, it's complicated."
Thing is, kids are best equipped to handle the "it's complicated"s of the world. They don't have a framework for thinking about how things should be, and so while explaining the behaviors of adults in a "child-safe" way is very difficult, it's actually much easier to just talk to them about things as though they're an adult, but an adult who isn't very well-read and didn't go through many history or government classes. Talk to them as though they'll understand, but be prepared to take detours. Rambling long conversations that start with "why do I have to go to school" will naturally end up covering topics like economics, education, forces of government, maybe even how governments come to be in the first place. Don't worry about circling back around, or talking in a straight line. My dad used to do this, but the best part was that it always did circle back, and the circling back was always a crazy conspiracy theory.
Not to say that they weren't true conspiracy theories - explanations of how the country got started, how companies got founded, the founding of religions, basically anything having to do with schedule 1 substances, and of course the crazy idea that the government listens to our phone conversations and reads our email. These were some of the more down-to-earth, realistic theories. As a hippie, he did occasionally tend to attribute to malice what could easily be attributed to incompetence, but those instances are far too many to list here (or anywhere.)
What this did for me as a kid was to give me a healthy dose of skepticism. First, I believed everything my dad said, but because that was often inconsistent with what I learned in school (my favorite was that we were teaching The Bhor Model in the 4th grade when it was so clearly didn't explain fine structure I mean what the hell) I started to realize that the narrative being sold by my school miiiiight not exactly be the cold, honest truth. I grew older, and after realizing that not absolutely everything my dad says is true but that most of his ideas were based on what he had learned and experienced in his lifetime, I began to accept that everyone might be like that. In fact, it might be that most people can only speak to what they have actually experienced, and everything else is just hearsay. This was a big thing for me, and it's what allowed me to summarily brush off people when they said I couldn't do things. This lesson is hard to teach, and it requires you being comfortable that your kid might form their own opinion, and that you might have to be the example when it comes to being wrong. I think my dad wasn't really afraid of that.
I will say, it has made me a good student of history. For a large portion of my life, I couldn't really study history to save my life (or grades.) After realizing that history is full of conspiracies I started to pay attention - the revolutionaries, the shady back-room deals, the murders, the lies, and best of all the successful cover-ups that we're only just now uncovering. Kids love that stuff - the more complicated, the more twists in the story, the more drama you can tell them, the better. They love, and can follow drama. Children are better at following drama than most adults, even if they don't have the reading comprehension skills they need to have. Telling them a story about the JFK assassination, or the Louisiana Purchase is riveting. Planet Money has amazing podcasts that explain the recent banking crises, which will easily get kids into current events. Explaining the reasoning (and maybe some of the action) of the Civil War will awaken the political scientist in your 10-year old.
I for one, tell my 10-year old all about conspiracy theories. Hopefully, he'll pick up the same skepticism I did. He frequently proudly announces when he's come to a conclusion opposite mine, and I'm proud of him for it (and then we get to argue.) I'll let you know if I catch him with a Dan Brown novel.