I'd say if his parents want him to learn about the Christian religion then he should go and listen and make up his own mind about what is taught. I would then institute a campaign to teach him critical thinking at every opportunity. Hallowe'en is a good one to teach the questioning of superstition. I did this with my grandchildren from the age of 6 and they both left the religion they had been raised in and became atheists by their teens.

Sometimes kids are looking for avenues to speak rather than be told. Of course, all completely depends on the child's age. I'd first ask him what he wants to do, then facilitate his talking about that, allowing him to formulate his picture (which, if young, is pretty Simple). Empathize. If he's interested in Your opinion, he can ask. Sometimes speaking our beliefs can only be confusing & add to the weight he carries regarding living in & pleasing this world of adults.

I would tell him that is a decision his parents have to make and leave it at that.

I think we owe a duty to truth to speak it as we know it. To be silent is to acquiesce to the lie.

Be honest & explain. Kids are a lot smarter than anyone gives them credit for & can smell a bs cover up a mile away. There are "universal truths" like being kind to others, being honest, not stealing, helping people in need, etc..all parts of the social contract. All the other exclusionary & "faith not fact" stuff...thats the sticking point.