My thoughts exactly, Daray and Radiance.
I don't think it's about "talking about your sex life". Kids usually know their parents have sex, that's just the way it is. That doesn't mean parents talk to their kids about having sex. They just talk about loving each other. And I can't imagine loving more than one man, but only telling my kids that I love one of them. That doesn't seem like a good example for kids, either, because if they find out, it will seem like I'm telling them "you should hide some of your friends" or "it's okay to be ashamed that you love some people".
That's not the kind of message I would want to send.
And of course, when they do realise it, even though I'm poly now and no kid has been born, well they'd feel betrayed and lied to for all of their lives, and like I'm a different person than the one they trusted. And that's pretty harsh too.