I'm quite enjoying this thread, very interesting stuff!
I think "poly" is a convenient term as it's the word many of us put out there, specifically "polyamory". In truth, I think a more simplified definition is "non-monogamy". Perhaps we are reluctant to use this definition as it can be associated with mono folks as swinging, cheating, fucking everything that movies, etc.
Our desire to be included with our heterosexual, monogamous brethren means many poly folks will strive to point out similarities between their lives and mono lives. Poly folks have jobs, children, spouses, pay taxes, etc. just like their neighbours. May I suggest that any divide between parents and child-free poly groups is that child-free folks can be viewed as those deviant, fuck-everything-that-moves types because if you aren't in a relationship to produce offspring, then your relationship is based purely on sex, right? (I'm being sarcastic by the way...) This is a very broad generalization and by no means intended to offend anyone. It's based on my own personal experiences with my own child-free status, coupled with being poly, I've had certain people question why I choose to be legally married.
The comparison that comes to mind is the reluctance of some of the gay community to accept bisexuality. There are gay folks out there, for whatever reason, who do not readily accept bisexuality. Lets not forget a few of the ignorant heterosexual crowd who believe bisexuals are just "confused" and haven't made up their minds yet. The community strives for acceptance because they still face a great deal of prejudice. Showing the world how "normal" they are perhaps means rejecting some of the variation that comes with sexual identity. It's sad really and I don't know what the solution is.
Poly is a big word really, with so many variations. I enjoy being able to openly discuss my partners with fellow poly folk and have attended some get togethers. The sense of "community" is nice to have, but in all honesty it's tolerance from my greater community that I would appreciate more. The day when being poly isn't viewed as something deviant, freakish, a source for gossip, and cause for judgment, would be a welcome day indeed.