C'mon, friends, we can be more helpful than this.

One 'girl to another, , although I haven't been through the US recently (with or without children), based on reading this board for many years, here's the advice I would give my own family in this situation.

You should not have to show ID for an 8-year-old, but someone may ask, as noted above. In case this happens, either you or your sister should take control of the situation (sounds like it should be you) and answer for your niece that she doesn't have (or need) ID. Don't be apologetic or embarrassed, just be firm. Part of the TSA's silly game is "behavior detection" where it's more about how you act than whether you really have an ID.

Explain to your niece that someone may ask her questions (name, where she's going) but that she doesn't have to answer. Again, one of the adults should firmly reply "why do you need to know that? Her name is right here on the boarding pass." Don't let them intimidate you.

You mentioned scanners. Your goal is to (a) get in a line where you can go through the WTMD rather than the NoS and (b) get through without setting off the WTMD. This gives you the best chance to avoid a patdown. Your niece will have to go through the WTMD on her own, but assuming she doesn't set if off, you should be able to stay fairly close together.

There is a chance that even if your niece doesn't set off the WTMD, she may be chosen for a patdown. There is a good chance that, even if she goes through the NoS, she may have to get a patdown afterwards. So using the body scanner may sound like a painless way to avoid the patdown, but it's not. If she gets selected for the patdown, you or your sister should be allowed to be nearby. Again, be firm. Under no circumstances should any of you agree to leave the checkpoint area to go to a "private room" for a search.

As your sister is a nervous flyer, I would arrange, well before you get to the checkpoint, that she go first, and is responsible for watching your belongings as they come out of the x-ray. You should then stay with your niece through the checkpoint. It is very likely to be painless, but you should be prepared for what might happen.

I assume you're flying from RDU to BOS, so choose your line carefully. This thread: Complete List of Airports with Whole Body Imaging/Advanced Imaging Technology Scanner says that RDU has:
Translation ()Terminal 1 has 1 millimetre-wave (radio) NoS. The checkpoint for the Southwest Airlines end of terminal 1 has 3 WTMDs on the left side and a NoS on the right. Terminal 2 checkpoint has 4 millimetre-wave NoS. So it sounds like it should be possible in Terminal 1 to avoid the NoS by choosing your line carefully. Terminal 2 could be more difficult. (Can someone with more knowledge of RDU advise?)

And for BOS:
Okay, I'm not sure exactly what that means. Do all these terminal at BOS, except the left lane of the Terminal C UA checkpoint and the VX checkpoint, have the NoS?

Good luck, and as Elizabeth said earlier in the thread, probably it will be no big deal, but it's good to be prepared.

We will be flying Delta which Terminal 2. I fly out of T2 every few weeks and at slow times they sometimes have EVERYONE going thru the scanners, other times it is about a 50/50 chance. There is no way to be sure that you won't go thru them. I ALWAYS opt out, well, actually, the last 2 times I flew I have pretended to not hear/see them when they pointed me towards the scanners and just walked thru the WTMD and kept going towards my luggage and neither time did anyone stop me, LOL.... Not sure what my sister will want to do. She hasn't flown in almost 2 years so things are much different since she last flew. I have discussed it with her and she is very opposed to the scanners but I have suggested for my nieces first trip to do whatever gives us the least chance of her getting felt up by the freako pervs. But, I will prepare her for it just in case it does happen. I really hate that I am having to have to have this discussion but I don't feel that not flying is an option. I will not let the terrorists (meaning the TSA) completely scare us off from flying.

Thanks for the replies.

Also keep in mind that the scanner technology at the two airports is very different. RDU has the RF MMW scanners which are almost certainly harmless and have less resolving power. So the resulting images are not as clear and detailed. BOS has the xray scanners which are almost certainly not harmless and the resulting images are clear, detailed, and very explicit. The consequences in terms of both privacy and health are more serious. Just something to keep in mind when deciding whether to opt out.

Well, Terminal 1 has 2 checkpoints, one at each end. The Southwest CP, described as having a MMW, is one I haven't been through in years. The other CP, presumably Air Tran and Jet Blue and whoever is left in T1, did not have a NoS of any kind at the end of Jan. I haven't been through there since US Air moved to T2, so I can't stand by the accuracy.

On occasion, if a person self-selects a WTMD line to stand in, a TSA agent will pull the person out of the WTMD line and direct to them to a NoS machine for one of a variety of reasons (random selection, keeping lines moving forward, or other nonsensical clap trap).

To mitigate the chance of being pulled into a NoS line, I have taken to wearing a sequined tank top or shirt when flying. I got the idea from a post somewhere in this forum a few months back. The thought is that the light reflections off the sequins will damage the ability of the NoS to accurately picture you, thus rendering the scan useless to them in their security quest.

My thought? A sequined tank top or shirt will redirect them in a non-confrontational way to leave me alone and let me go through the WTMD.

So far so good, including randomly pulling my colleagues I'm working with out of the WTMD lines around me to go through the NoS.

My suggestion is to get a cute sparkly shirt or tank for your 8 year old niece as a special shirt for her to wear for the flight. Here's one to get you started. Remember that it has to be a shirt, and not a jacket or a sweater since those may have to be removed.

Good luck!