"How do we know there's no God?" My 9-year-old daughter, the youngest of my three children, was doing her math homework in the kitchen and must have overheard her father and me talking. I hesitated. Even though I'd been raising my kids as atheists for most of a decade, I was caught off guard.

My firstborn, Noah, never questioned me on the issue of a Supreme Being; he was more concerned about his Jewishness. So what if God was pretend — he could still have a bar mitzvah, right?

His younger brother also accepted God's fictional nature, but he gave me hell about heaven. Brooding on mortality at age 6, he pushed hard for the possibility of an afterlife. "We don't actually know what happens after you die, right?" he said. "I mean, you can't talk to someone who's dead, after all. There could be a heaven." Still, no matter what solution Jesse temporarily embraced — um, reincarnation? — it never included God.

The boys are 14 and 12 now. They glance at me slyly during the "under God" part of the Pledge; at their grandparents' Seders, they read aloud passages about the Burning Bush like overenunciating actors rather than believers. Done and done.

Lena is 9. She is not worried about death and she's not interested in being Jewish. She just wants to know how the world works. She asks everything: How long do chickens live and what is insurance and how do you remember the way to all the places you drive and how do girls masturbate?

I answered all of these. The God one should be relatively easy: It's a question atheists get asked all the time, usually by people who think we should use the gentler term "agnostic," people who are comfortable with doubt, but suspicious of certainty.

To them I would say that all evidence points to the fact that God is a popular and useful fiction, and that no evidence points to the fact that He actually exists.

And where's the evidence that He doesn't exist? That's what Lena's asking for. And that's what leaves many people in the "agnostic" camp and (understandably) makes many parents — even those willing to be counted as atheists themselves — wary of issuing definitive statements to their children.

The few books that offer advice to atheist parents counsel us not to be definitive. They tell us to let children decide for themselves what they do or do not believe. This seems perfectly reasonable. As open-minded, educated people, we should let our children decide for themselves, right?

I looked at my daughter, the fourth-grader, pencil poised over mixed number problems, head cocked, waiting. Should she get to decide for herself? No one told me God didn't exist. I grew up Reform Jewish and bookish. Technically, I guess, the prayers we said in Hebrew to bless the wine on Friday nights were addressed to an actual being. But when we talked about God, we spoke of Him as a fascinating literary character rather than as a real force in our lives.

So I have no memory of believing in God, even at my bat mitzvah; at my Jewish wedding we studiously avoided invoking His name. But it wasn't until I had children that I realized I had to spell it out: God was a compelling fiction created in response to human need.

That was enough for my boys, and I had assumed it was enough for Lena. But I had been wrong: She needed more. And it was my solemn responsibility as a parent to give her the information she asks for, to help her understand the world.

For that reason, it would never have occurred to me to let Lena decide for herself whether vampires exist (although there's no evidence to the contrary), or fairies or leprechauns, or all the denizens of Mount Olympus — even though some people at some point believed the Greek gods were real.

Fairies and Ares are magical, invisible beings whose existence cannot be disproven. Just like God. Logically, they are the same. But culturally? Emotionally? Not even close. There may be a whopping 3% of us atheists now, but it's still a believers' world.

We live in a culture in which at least 74% of us believe in a personal God, more than 40% of us believe God created the Earth 10,000 years ago, the calendar is counted from the birth of a deity (and the months are named for other, passé deities), our money states "In God we trust," witnesses swear on Bibles, and major political speeches end with "God Bless America."

In this context, it's hard even for me to remember it's all made up.

When I feel that way, Greek gods can be a helpful corrective, a reminder that just because a belief system is ubiquitous doesn't make it true. At some point, people were building temples to the Greek gods and atheism was a capital offense. And even then some brave mother managed to murmur to her kids, "Athena's a cool idea, but believe me, she's just pretend."

Take a breath, I told myself, step outside the believing world for a second, and tell your kid the truth.

How do we know, Lena? We know the way we know there are no fairies: The only proof is man-made and all the thinking behind it is wishful. We know because we are open to evidence and we have been given none. We know because —



But she had gone back to figuring out how fractions work.

Done. For now, at least.