I would be pissed if another parent assumed my kids were religious and tried discussing religion with them. And that's the problem with the religious. They assume everyone believes in god, so they don't hesitate to inject their thoughts about god onto any other person they see. That makes them dangerous in the fact that if they freely talk about god with an adult, they'll do it to kids. Even those not their own.
Disclaimer: I am only responsible for what I say, not what you choose to understand.