Well, personally I am relatively lucky here. I've always liked flying/airports (and that's my future career), so I don't really have a problem with it. Though TSA is getting a lot of bad press now... Just a heads up, you know that those backscatter x-ray scanners are called x-ray for a reason.... Not very well proved safe. But the MMwave scanners seem to be safe for now. For those wondering, the flat panels you stand between are BackScatter XRay, and the circular booths are MMwave scanners (correctly known as millimeter wave scanners). I had no problem traveling to Canada in august, though I forgot my (metal) belt and therefore got wanded and "zapped" (MMwave scanner) thanks to that o_o. Though at that point Saint Louis did not have scanners yet, so easy going there. And customs went great (like, we were extremely lucky and had no line, no problems). If your kid has a problem, try to calm them, and try to use the scanner (though you might want to stay away from backscatter XRay ones). I must warn you all, the TSA is now going to use MUCH more invasive patdowns, so be careful if traveling with your kid, and try to meet your kids needs. Hopefully this info might have helped.
EDIT: Toronto has scanners too, a few Canadian airports gave them. Toronto had MMwave scanners.