My thoughts too. The whole proton precession and resonance thing, plus how it is actually encoded into images is just so clever. Obviously it’s been a very useful, life-saving tech…but I also just appreciate it as an engineering marvel in itself.
The Nobel Prize in Physiology or Medicine 2003 to Paul C. Lauterbur and Peter Mansfield “for their discoveries concerning magnetic resonance imaging.”
I think @enipla’s question has been answered 
I get yelled at by the tech if I do, as I tend to move around as I fall asleep.
My CT scans have always been short, my MRIs are never less than 30 minutes and have taken as long as 90 minutes in the bore.
Sorry I guess my recollection of the typical clinical times is out of date, or was always inaccurate.
But boy, I’d hate to see someone with claustrophobia trying to stomach 90 mins in there. Or a child.
In a child?
I’ve had a few. The machine is noisy. It’s boring. Usually, you can lie in a position that is physically comfortable.
I’ve never had anyone in the room with me, except right at the start and at the end. But they gave me a bulb to squeeze if I needed them to stop, and there was a loudspeaker system so they could talk to me between images. I think once I really wanted to move something, and asked if it was okay, and I wriggled a bit, said I was set, and they started up again.
I don’t think anything horrible happens if you move, it just ruins that pass, and they might have to re-do it.
If you don’t need drugs, it’s easier to skip that – no drugs mean you can drive yourself there and back.
You’ll be fine.
I had a chest MRI after my breast cancer diagnosis in 2017, and I was face-down, in a semi-open unit, and dropped my breasts into coils. I also had my choice of music; I selected classical and enjoyed that via headphones while the machine clanged around me.
p.s. It took about 30 minutes, the first half without contrast, and the second half with it.
Pre-teen children are probably going to be sedated anyway, so they will lie still.
Too dark to read in there.
Another thought.
After I posted early on, I didn’t read the rest of the thread, so I don’t know if anyone mentioned this but: you can’t wear anything metal. If you do have on anything metal on, you have to take it off and they will want you to put on the highly ventilated hospital gown. 
So the couple of times I’ve had an MRI, I wore elastic-waist pants with no buttons or zippers, a t-shirt, 100% canvas/fabric shoes (Sketchers), no watch, no earrings (not even the diamond stud that my late husband gave me for Christmas 33 years ago that I never take out), no jewelry of any kind. Of course, no glasses or hearing aids. NO METAL.
When I tell the techie person that that I have no metal on or in me, they let me get in the machine with my regular clothes. You feel more comfortable, less vulnerable. (And warmer, if that’s a concern.)
“Outside of a dog, a book is a man’s best friend. Inside of a dog, it’s too dark to read.”
-Groucho Marx
Don’t know for sure; but in my case they told me that I mustn’t move my torso because they needed to be able to compare images taken with me in the same position, so moving the area they were trying to image would ruin the entire run.
They said IIRC that very slightly moving my arms or legs was OK.
I had a series about twenty years ago. It was just loud and dull. Once I got used to the banging, I managed to fall asleep.
I then learned that I have some serious brain damage. Naturally, my sister said she could have told me that for free.
I had one several years ago. They piped in music as they did the scan. Not a problem.
I had another this year (and will again this month), but that’s checking my abdomen, so claustrophobia isn’t an issue.
I’ve had several over the past 5 or 6 years. No biggie.
I’ve had way too many. I had no problem with them until one time I did. Now I get my doctor to prescribe one dose of Xanax for me. I think it started when I had a shoulder MRI and I had to wear a cage and barely squeezed into the tube. I’m pretty broad across the shoulders. I’m fine as long as I have an inch on either side of my shoulders. Not all MRIs are the same. When I’ve had to get brain scans they requested a 3T machine. That was wide enough that I wouldn’t need any medication.
Claustrophobia runs in my family…yay heredity! Anyway, I thought I had escaped since I made it to mid-40s with no issues. I camp and backpack a lot and one night I woke feeling like I couldn’t breathe/get air. In a tent. Not much later I had to get an MRI, which was my third, and I never had an issue with the previous two. As soon as my head went in the tube I went into mild panic mode. The tech noticed and pulled me out. He suggested putting a folded up small towel over my eyes which helped enough to get me through the MRI but it wasn’t pleasant.
I’ve since had a couple more episodes in our tent but it’s eclipsed by the back pain. I used to sleep on the slimmest closed foam pads soundly in my 20s and 30s. Now I’m up to a 3" air pad and still wishing I could carry a real mattress. Mid 50’s and wondering how long I can backpack. When I get an “episode” in a tent, I go water a tree and that is all it takes. I’ve tried sitting up and reading but that doesn’t calm my mind enough.
I think I can manage no metal except for a bra. All of mine have metal hooks and eyes at the very least. I suppose I’ll have to disrobe on top.
You’ll definitely have to take it off, and leave it outside the room.
If you’ve got time, get a pullover version for the day? Depending on your size, some of them are cheap.