Again, a key point is sometimes being glossed over.
I don't think it's necessarily true that atheists bring their children up to "be" atheists in the same way that Christians, usually, bring their children up in the faith. For one thing it's a bit difficult to define what you do to "be" an atheist - there are no observances to follow, no incantations, rituals, beliefs to express, utterances, texts, symbols, places of gathering/ education or events solely for atheists. It's something defined by what you are not - a believer in gods.
I don't think it's possible for me actively to bring my children up to be atheists. But maybe teaching them that Bible stories are to be regarded on a par with Greek legends and Norse mythology is doing so by omission? In that case, I am.
I'm teaching them, I hope, to be sceptical of anybody who makes claims with no evidence.
Atheism, as stated above, is not a faith-based position. No, it isn't. No, I'm sorry, but it isn't. It is an evidence-based position. You do not believe in God or gods because there is as little evidence for them as there is for a flat Earth, tealeaf-reading and the moon being made of green cheese. If you want to give your children the opportunity to encounter religion on the basis of "letting them make up their own minds" when they are older, you are on a hiding to nothing - if you are going to do that, you need to give them access to all known religions and also to Breatharianism, the Moonies, that David Icke cult and the whole damn lot of them.
In fact:
here's the whole damn lot of them!
My mother thinks they "need" religion, "otherwise how are they going to know what's right?", and that's partly why she was quietly fuming when we didn't get DD or DS christened. She thinks this means they are not going to get any moral instruction in their lives, which I find hugely offensive.
I hope they will grow up with a healthy scepticism, and to be suspicious of being part of anything which claims to have the answers, that one Way is the only True Way, that one book is the only True Book, that one god is the only God, etc.