A good bet is alternative media, things like kurzgesagt, verisitium or other science outreach programs.

The other thing is education, engage with his education, and teach him yourself to think critically.

And I hate to say it to say it, but religion conditions kids to brainwashing. Even if not extremists.

Feel comfortable pointing out flaws in Christianity and question them with him.

And lastly, try not to be argumentitive. You need to carefully tease him out of these beliefs, not destroy them.

That would feel like you are attacking him and will probably be counterproductive.

Best advice I can offer is to ask questions whenever you hear something objectionable.

Child: "You like science too much."

You: "Why do you think that?" or "Why do you say that?"

Asking them to explain what they are saying tells you more about what is really going on and can help them to consider why they think that way.

This guy is who I have in mind when talking about this subject. https://youtu.be/9gHmhObfbn4?si=xKaMUCh37q_UOxjo

The best way to combat biblical literalists is make them read and study the Bible. It's a self-contradictory book of folk tales. Once that's clear the rest will sort itself out

You can’t fight brainwashing by providing more facts. It doesn’t work. Brainwashing gives the victim mechanisms to reject new facts that contradict the false beliefs. The false beliefs become a part of a person’s identity, so it’s tied into self esteem and confidence. So that’s how you have to approach it: find ways to challenge the false beliefs that don’t also challenge their sense of self. For adults this is very difficult.

But for children, it’s easier. During the teen years children are trying on identities like they’re trying on clothes. Give you child a look at a good, comfortable identity. It should make them confident, give them a community they feel comfortable in, and not make enemies of the ones they love.

I find that scientific skepticism does this by giving people the tools to think rationally about the world, spot ways that the world tries to deceive them, and giving an understanding of why those deceptions are effective.

Part of what is going on is probably survival mechanism. You have to question, does child feel safe to disagree at other house? Because that might be the cause of the entrenched views. Kid can't question the beliefs, even away from there, because they would smell the doubt and it's harder for kids to hold one belief and lie. Just make your home a safe space, and ask questions, so many questions. Let his mind hold those questions in the background and one day they'll unlock his mind from that brainwashing. Just build him up, make your home a safe space for anything. Question your own beliefs, don't just do that to his, ask questions about everything. Be open to saying this is just a belief, not fact. And that it's still OK to believe, but knowing the difference between belief and fact and they can both exist. Don't challenge the individual thoughts, teach him how to critically evaluate something, don't just give him a fish, teach him how to fish. I wouldn't challenge his beliefs at all, I would focus on other things and question those, avoid conclusions. Let those be unsaid, for now, or let him come to them. If he is criticising your beliefs, (saying you believe in science too much) you are a safe person. Just make sure they don't reel him over there full time, keep your time, maybe even try and get an extra day or two

Why do all the scientists lie? What do they get? How do they get convinced to lie? Research who pays them, if it's money. Ask as if you want to know, not to debunk. Be interested. Which sciences are fake? How do you tell which are fake? Who decides what's true and fake? If you delve deeper into any of the things they don't hold water, but don't say that. Just let that uncover itself. Make space for him to have his beliefs and respect them. Arguing for him to abandon his beliefs will just push him away.

I think you gotta be more fun about it. Kids aren't gonna care about books and documentaries, they'll be so bored. I enjoyed science through magic school bus, jumpstart, Bill Nye, mythbusters. I don't know what they have now, you might have to do some searching. Stand up comedy is also good for social critical thinking and it's fun. Don't bore your kid into the wrong path lol.

Did you know, kids who grow up with parents who disagree with each other learn critical thinking skills quicker than other kids.

YouTube channels like Veritasium, Steve Mould, Kurzgesagt, SmarterEveryDay, or Hank Green are really good places to start. But you should also try to get him involved in hands-on things like science fairs, science clubs at school, visiting museums, etc.

The goal isn't necessarily to get him to think critically right off the bat, but instead get him excited to learn and curious about how the world works. Manage that and the rest will inevitably follow. Also, have patience and don't preach (not saying that you are, it's just something I have experience with), there is no faster way to kill excitement than to make someone feel like they are forced to do something.

Maybe go to a museum. Hard to deny cavemen existed when you can look at their bones and see their tools right there in front of you.

You helped to brainwash him by already In doctrinating him with religious dogma. You should start by teaching him critical thinking skills and help pull him out of that dumb bullshit.