Oh, it's a stressful job alright - if, as Enid says, you take it seriously.
Most of us do. It's those who don't who give the rest of us such a terrible reputation.
We have all the responsibility during our couple of hours that the teachers do, with none of the training, none of the respect, and without being able to discipline the children in the same way as the teachers can.
Today I was outside in the playground. I acted as a counsellor to a child who is having a shitty time in an abusive home, referee to several children who were hell-bent on strangling each other, shoulder to cry on for several children who are having difficulty settling in. We are also expected to be nutritionists, mediators and punchbags, and put up with being spat and and sworn at most days without raising our voices or becoming angry or upset. I have horrible scars up my arms from being attacked by a Y2 child - a six year old - last year who decided he was going to sink his teeth and nails into me because I pulled him off a boy he was trying to strangle.
When we are outside, four of us have to supervise 270 children - and without those eyes in the backs of our heads which would be so very useful, it's impossible to watch them as closely as we (or their parents) would like. And when someone is hurt because we were dealing with something else, or because those eyes in the backs of our heads weren't working, we bear the brunt of the parents who have only heard one side of the story and believe the popular idea that we are all thick as pig shit and get off on being mean to children.
What people often forget is that we get the worst behaviour of the day - when they aren't sitting down in one place being given a task to focus on. We see them letting it all out, and their behaviour is not the same as it is in the classroom. They fight, they push, they hurt each other. They often don't listen to what you are telling them, and if you tell them once not to climb that tree/pull those plants up/kick that child you will still find yourself telling them again and again and again and again ... it's like banging your head up against a brick wall, but without the relief when it stops!
There is one particular duty I have to do which involves supervising the Y2 children playing football, and they are more violent with each other than you would ever believe possible. I hate my job that day; I regularly come home and spend the afternoon in tears at the way the children have behaved to me, and the way I have had to talk to them to get them to listen to me. And this is a nice school with (mostly) well-behaved children in it.
There is also the fact that children don't always tell the whole truth about us. One mother came in all guns blazing once, because apparently I had handcuffed her son to the railings and made him stand there all lunchtimes. We don't have any railings, we don't (unfortunately ) have any handcuffs, and although I had spent the entire lunchtime trying to stop her son from beating the living daylights out of another boy, I hadn't so much as raised my voice to him.
Yes, it's a short shift. But it is hard graft, and it is more stressful than I would ever have believed it to be.