If you see another child in your class or playground crying, shouting, screaming or maybe on the ground, then they could be having a meltdown. This is not a tantrum, to get attention. This is usually because something has either upset them or have had a sensory overload. It could be because they have been bullied by another child. Or it could be because there is too much noise, too many people around them, too many smells, or in all too much stimulation around them for them to cope with.
If the child is being picked on, then please tell the teacher. Bullying in any way is not OK and should be dealt with.
So, what to do if you do see a child like this? Here are my ideas:
1. Tell a teacher or assistant you can see in the playground
2. Give the child space
3. Don't ask the child if they are OK.
4. Try to get other children not to interfere and tease
5. Does the child like something such as a toy? If so, maybe you can suggest to the teacher they take it to the child.
Please note that I am not an expert and don't have a degree. I am just going by experience and what I have read by experts.