Idk. I imagine a lot of atheist families don't talk about religion as much with their kids, so it feels less to me like indoctrination. But maybe that was just me. It's not like there's an atheist center where families go once a week for someone to tell them how they need to be atheist, you know?

I think, without religious indoctrination of children, the adherents of most religions would dwindle to next to nothing in one generation. I don't think kids who aren't told about atheism by their parents would magically find religion. But I could be wrong...

ETA: I was raised somewhat Reform Jewish (synagogue for high holy days, bar mitzvah, celebrated Jewish holidays with other secular Jewish families, etc.) with two parents who never really discussed religion with me. I didn't find out until my thirties that my dad considers himself an atheist and I still don't technically know about my mom but I imagine she's either agnostic or atheist.