neighbor wants to take our baby to church

Stephanie
My baby is 8 months now, and our neighbors across the street are an older black couple whom we love who occasionally babysit him and treat him like their grandchild.  They lost their only son when he was an adult.
They're very religious, and we're atheist, but they don't know and we'd like to keep it that way.  However, recently our neighbor mentioned that they want to take him to church sometime.  I'm soo uncomfortable with this, and I'm not sure how to respond.  They are amazing and help us out, so I don't want to burn any bridges, but I also don't want my child to be brainwashed at an early age.