That's a surefire way to piss off anyone who is truly childfree in about 1 second flat.
Anyone who says this is not childfree, and never was. They were childless.
You might be saying to yourself "what's the difference?" Someone who is childless doesn't have children right now, but wants to (or might want to) have them at some point in the future.
Someone who is childfree never wants to have children, ever. Not biological children, not adopted children, not step-children.
If you would be ok with adopting, you are not childfree.
If you would be ok with dating/marrying someone with children, you are not childfree.
If you don't want children right now, you are not childfree.
Someone who is childfree doesn't want kids now or ever. Not their own, and not somebody else's.
And you are absolutely, positively not childfree if you dropped your kids off with the grandparents for the day.