I also just came across this article randomly, so never say never, right? Maybe OP's fears are not entirely unfounded...
"Police searching for man who grabbed 12-year-old boy in south city McDonald's bathroom"
http://fostercity.patch.com/article...-mcdonalds-bathroom?ncid=txtlnkuspatc00000003
This does happen quite a bit more than most people realize. Remember, I had a job where I actually had access to these things beyond what the media reported. The media actually reports very little of this stuff.
And guess what else? People DO ignore kids yelling. Frequently. They don't want to get involved. Or they believe the kid is fighting with his/her parents. Or they think the kid is special needs. If people even notice. When it is crowded, and loud, and people are in their own little bubble, people don't even notices.
And even responsible, smart kids do bone-headed things. Have you ever met an 11 year old boy? Their hormones are up and down and sometimes their brain cells get turned off. We work concessions at the high school football games for fundraising (three high schools share the stadium) and the things you see kids do... Yikes! My thoughts are always, "if your parents only had the slightest clue, you wouldn't be allowed here again." MANY of us feel this way. And I do personally know some of those kids and their parents, their parents have no clue and would be mighty upset if they knew what their kids were doing behind their backs.
Yes, his feet are bigger than mine. Yes, his voice is deepening (on and off). No, he is not quite 5' yet though. If he were man-sized, I probably wouldn't bat an eye.
Yes, as a kid my sisters and I wondered WDW by yourselves (9, 12, 14--I was the 9 year old), but not only are girls more mature than boys, there wasn't as much there and ways to get around. Yes, last November I did let him and his brother (then 10 & 7) go on rides alone so I could sit out with the sleeping baby and DH could take DS6 on something more to his liking. But I felt he was somewhat supervised--not out in the open.
I'm not refusing to let him grow up. Most people who know me would say I'm very relaxed. Heck, when he's 14, I'll be dropping him off in the woods with a couple days supply of water, a fire starter, and a compass (he's a Boy Scout). I just like the idea of some semblance of supervision from somewhere while he is still little, and 11 is still little--that is why BSA says boys must be 14 before they can participate in certain activities. Especially knowing how long the lines can get in the restrooms.
He have an iphone for when the kids go someplace without us in case of emergency (it's a "family" phone) and he will certainly have it with him in the parks in case we do get separated or something happens to me. No, I will not be on it with him in the bathroom (although it's a good ease your nerves suggestion).
What I will do is send him to the restroom when I need to go and then meet him in the nearest gift shop. I don't trust other guests, but I do trust CMs to pay attention. I'll send him a text when I'm coming out and he can meet me by the register. It gives me the feeling of confinement for safety and him the freedom to grow up--which should, imo, happen little by little.