There is a huge difference between NOT using the label "atheist," to self-describe, even though you are an atheist, versus denying that you are an atheist when you are asked if you are an atheist.
There is, in fact, a label for couples without children. That would be "childless." You are free to say "I choose not to have children" when asked if you have children. But it would be dishonest to reply to someone who asks "Oh, then you're childless?" with "no." It would not only be dishonest, but confusing--considering that you are, in fact, childless. The correct response, based on your position, would be "I am childless, but I don't like labels. So, I just like to say I choose not to have children."
Some people don't self-describe as atheists, but when asked point blank, they also don't lie--they just notify the asker that they don't like to use labels to describe themselves. Other people who don't believe a gods exist actually DO deny, dishonestly, they are atheists. These people are either lying or ignorant about what they are.
I hope this helps.