1) a. Are step-parents childfree?
No, because they've chosen to have children.
b. What if the step "kids" are grown?
That's kinda iffy. If the kids are out of the house and no longer being supported whatsoever, it can be a yes. But it depends of the personal viewpoint.
c. What if they were step-parents, but later broke up?
I'd say childfree.
d. What if they're in a relationship with someone who is a parent and that parent has zero custody or involvement?
Childfree.
2) a. Are people who are open to being foster parents childfree?
No
b. Are people who actually are foster parents childfree?
No
c. What if they did this at some point in the past, but no longer do?
If they are going to foster later on or have kids, childless. Otherwise, I'd go with childfree.
3) a. Are people who are open to taking in their younger siblings or sibling's kids or other children in the family childfree?
Younger siblings, depends on the age. 16+ I'd say you're still childfree. Under that you're just childfree at heart :)
Other children, not childfree.
c. What if they did this at some point in the past, but no longer do?
Same answer as 2c
d. What if custody was only temporary?
Same as 2c
4) a. Are people who have a baby but give it up for adoption childfree?
I'd say so.
b. Are women who do this childfree?
Yes
c. What about men?
Yes
d. What if the man never even knew about it?
Then he's childfree
5) a. Are people who had a baby which died in infancy childfree?
If they still want children they're childless.
b. What if it died shortly after delivery or was stillborn?
Same as above
c. What if it was a miscarriage of a pregnancy that was intended to be carried to term?
Same as above
d. What if it was a miscarriage of a pregnancy that would have been aborted anyway?
Childfree, unless they plan on having more children later on in life
e. What if any of the above happened, but the intention was to give it up for adoption?
Childfree unless they planned on having kids later in life.
f. For any of the above, what about a man who never knew about the baby or the pregnancy?
He's still childfree
6) What about host families for foreign exchange students?
Not childfree.
Whew. Hope this answers your questions!