Has anyone's child been put in one when he would not calm down or stop crying?
I'm speaking from the teaching end of things. It happens, and I've seen it done in some of the schools I've worked at. However, it is rarely appropriate for a non-aggressive child in a regular school setting. Generally there's almost always a better way of managing behaviors when kids have meltdowns/outbursts than locking them in a room. When you have the kinds of kids who are unable to cope either in a mainstream environment (regular classes) or in a self-contained setting (a special education classroom), that's the stage when other placement options should be explored. It is my opinion that the practice of having "safe rooms" in a standard public school environment should be completely abolished because they're a technique intended for a more psychiatric/restrictive setting and public school employees as a rule do not have that kind of training or experience, and should not be pretending to have it.
What would you have done?
As a parent, definitely have a sit down and figure out a better way of managing the behavior at school--whatever that looks like for your individual situation and the variables you have to work with.
As a teacher (I work with teenagers):
There's a whole continuum of possible responses of student behavior. I deal with a lot of it through prevention. I have a lot of communication routines that I use so I'm aware of who is already having a bad day before they even get to school. My room is set up in such a way that I can accommodate a wide variety of students and their varying needs. I have spaces in my classroom where kids can go "take a break" if they're getting overwhelmed (I always have quite a few students on the autism spectrum, a few who have anger management issues, and generally at least one kid with an EBD). There's places in the room where students can sit if they prefer to work alone, need less visual stimulation, or are out sight from the rest of the class. I keep calming materials for students who are using "time out spaces" so students will have something to distract themselves with while they're there (fidgets, sensory items, books about animals, pictures of puppies, etc). Usually a student who is having a problem can stay in the classroom. If they are so upset that they need to leave the room, there's a space right outside the classroom (where they can sit) that's easy to monitor, and I'll tell them to go take a break outside for a few minutes. I rarely have a problem with anyone wandering off. If someone has escalated to the point where physical violence/property damage is likely, I get then out of the room and take them outside for a few minutes (so if they need to yell/scream/punch the wall) it's no big deal because there's nothing to break/no one who can get hurt outside the building. (Usually what happens is they yell/scream for a few minutes, calm down fairly quickly, and come sit out in front of the room for a few more minutes, then come back to class). This is also easy to do and I can still see my classroom from this spot. We have a few counselors on site and if a student is having a major personal problem that they need to talk to someone about, talking to a counselor or the mental health consultant is another option.
Oh, and if for some reason the whole class seems "off", I take them outside for a couple of laps around the building. Works like a charm.
Only rarely do I get a student whose behavior requires me to bring in outside parties to help manage it. I have never seen a student NOT calm down--even some of the most severe ones I've worked with. I know it's possible, but I have never seen it happen in real life...and I've done plenty of time in EBD classrooms. If nothing else, you'd think they'd just summon a parent to come pick up the kid if they couldn't deal with them at school.
In other words, there are definitely more effective ways of dealing with students, even students with severe emotional and behavioral issues, than locking them in a room. I'm pretty sure of THAT.