Again, as I said initially, he is the type of kid who doesn’t want information he hasn’t asked for. It took he and I a long time to learn that, because I, as you may guess, am the opposite. I want to know everything about every possibility so I’m not blindsided by anything. He finds that anxiety producing and difficult. This includes things like what to expect post-surgery, what day is school starting (he asked me to give him a one week warning, but not to mention it before that this summer), what our schedule is for the whole weekend (he only wants to hear about it day-by-day, so he’s not thrown for a loop when plans change), what Grandma’s last stress test showed. In short, he has a very good grasp of how much he can handle, and will ask specific question which he wants me to answer and not offer a lot of other information until he asks for it.
As you can probably further guess, this took me a lot of trial and error to learn, as I tend to over-answer questions. 
I’m surmising, based on what I know about his tolerance for information, that he doesn’t really want to know whose dick his mother is sucking. Call it a gut instinct, if you want.
I will never, ever lie to him about this. The second he says, “Mom, is something going on with WhyDad and Rebecca?” I will answer him honestly. The second he says, “Mom, did you ever think about having an open marriage like X’s?”, I will tell him what’s up.
I am not lying, I am not even going far out of my way to hide it. I am being discrete, and I am refraining from mentioning things he hasn’t asked about because that’s what he’s asked me to do for many other areas of his life.
Now, since the rest of your questions pertain to a lifestyle I know nothing about, I’ll assume they are there for someone else to answer.
Now that I’ll agree with. Yes, kids **could **have a negative reaction if they found out their parents were poly. Absolutely. And, like every other rough patch in a kid’s life, I’d hope that the parents were there to offer love and support and keep communication open to help the kid deal with his feelings in a healthy way. Someday, someway, he’s going to be faced with the shock of finding out that the world doesn’t always work the way he thought it would. I do hope his parents help him deal with that.
I have never asserted that no kid ever could be troubled by being part of a “weird” family. I have simply asserted, based on my own experiences, that not every child is “devastated” when finding out her parents are poly.