I think it varies, so I'll just speak for myself here.
My kids (9 and 11) know my beliefs, but I'm always careful to couch them as 'my beliefs'. They have plenty of examples around them of opposing beliefs, both within our extended families, and from our closest friends.
We talk quite explicitly about the fact that people have different beliefs, and that my kids will need to work out what they believe. We also talk about how people with different beliefs can get along, and what we judge people on, etc.
It's all pretty simple, and doesn't take much effort, but my atheism came to me through consideration and thought over time. If it holds any value at all, it comes from that, rather than of it's own 'nature'. I'd be doing my kids a disservice if I taught them what's 'right' in terms of belief. I focus on open-conversations on belief, and judgement on actions.