I'm hesitant to use that phrasing since irreligion isn't a belief system as such - it's not a worldview. The only thing two atheists can agree on, presuming that all we know about them is that they're atheists, would be that they don't believe in a deity. We don't know why, what they do believe in, etc. - they could believe in any other superstition, e.g. ghosts if they wanted to, as long as it's not a deity. The same cannot be said for any other religion or ideology. My answer would be something like: teach no religion as the truth, but rather - a philosophical thing. I wouldn't take a child to church until they are of sufficient mental maturity to really choose, and by that time - they should be able to reason why they've chosen a specific religion and adopt its values. I'll always encourage them to think for themselves, with no bias towards any religion or irreligion. I'll offer my say in it - I won't impede their freedom to choose. In theory, it should bring them naturally towards atheistic views if delivered impartially. I'm fine with that.