Interesting question. I have fond memories of the Narnia series as well (although I tried to reread The War of the Worlds recently, something else I used to like, and couldn't stand it). I would say to let the kids read what they want, but to talk about it with them. I've been feeling a lot lately that one of the most radical things you can do with kids is just talk with them and listen to them regularly. I talk as much with my kids in a week as my parents did with me in a year.

Another poster mentioned The Golden Compass, which is great, although it actually has other issues. Its author is a reddit-style atheist whose hatred of religion is, as usual, just a cover for a hatred of Islam and the Global South IMO.

In general I think it's okay to consume problematic media, so long as you're aware that it's problematic. My younger kid and I have been watching horror movies lately (judge all you like) and even with the very best films, the issues are in plain sight. We just watched, and loved, Aliens, which I've only seen a couple of times and haven't watched in decades. After this viewing (and glancing through the film's wikipedia page) it became obvious to me that the xenomorphs are the Viet Cong and actually the good guys in the film? I've gotten some pushback on hexbear for saying this, but western art, especially after 1917, is defined principally by its anti-communism. A film like Aliens has a lot in common with zombie movies, the blob, Predator (even if the predator is more like a reflection of the marines hunting it, it still has a lot in common with a white supremacist view of anti-colonial struggles), etc., and all of this is tied to anti-communism. (Zombies, aliens, ghosts, any kind of horrifying Other is the world's BIPOC working class fighting back—but even in romantic comedies that strenuously avoid any discussion of politics, the specter of communism is always hovering in the background). We also watched The Exorcist, which, while a great movie, is basically a Catholic propaganda piece about how women's liberation is evil and disgusting. At the same time, it's a rare Hollywood film that, oddly enough, dares to show Muslim people just kind of hanging out and being people (in the opening scene). I suspect this is because the movie came out several years before the Iranian Revolution, when the USA was actually a little more ambivalent to the Middle East, but I digress.

Even a movie like Oppenheimer, which I also liked despite its many obvious problems, treats its main character's communism like a youthful indiscretion. ("Cancel culture is bad because corrupt elites tried to cancel communists in the past," according to a director who looks as though he dresses in a suit even in the privacy of his own home, and whose films are packed with dudes in suits saving the world.) It's extremely difficult to find western art that actually embraces AES, although I think this will change in the near future as the financialization of every last aspect of existence in the west leads people toward art that actually has heart and soul, which will be produced by the Global South. We recently watched and loved Godzilla Minus One, which was produced by an imperial core country, but which had an obvious anti-American message, even if the deeper message might have been "Japanese fascism is better than American fascism."

But there's still a lot to be gained from consuming this kind of media. It's important to be exposed to the world, not to be isolated from it. Ultimately, whenever our kids go outside, as long as we're living in the imperial core, they're going to be surrounded by this shit. They need to be exposed to it so they understand it. I do think there's some risk that it will contaminate them—my younger kid is more radical than my older one, for instance. The older read through the entire Harry Potter series years ago when I was a lib; the younger can't stand Harry Potter and has no interest in reading it. I radicalized when the older was around seven years old; the younger was four at the time and has had a proportionately heavier exposure to Marxism. (Both kids check all the right boxes, the older one just sometimes gets annoyed by political discussions.)

Still, having at least one major Marxist influence in their lives means that my kids will always have an explanation ready for why everything is collapsing and why everything sucks in amerikkka, an explanation that is deeper, more complete, and more scientific than any other ideology will be able to offer. Putting that ideology into practice (by analyzing art, for instance) can help to strengthen it and lead to its application elsewhere (perhaps by fighting in a revolution).