Small children (and many adults; and to some extent everyone) overreact when they get stressed: they become angry, self-centered, and incapable of measured logical thinking; they interpret incidental or minor problems as calamities; they lose sight of context and feel insulted by normally harmless comments; they ascribe their stress to totally unrelated causes. When multiple people are involved, and more than one is stressed, you get horrible miscommunication, and shouting matches where both people are convinced that the other one is a jerk.

As people grow up, they can learn to control their emotional response, or at least learn non-destructive coping mechanisms. (For instance, leaving an argument alone until both parties have calmed down enough to think about what’s really at stake in the argument and what’s important and come up with solutions that both can agree to.) They can learn the true causes of their stress, and try to fix those, instead of blaming unrelated people or events.

This is the most well-expressed comment I've read in a while.

Any suggestions for helping someone when they're in that state? Or for helping them grow such that these states are less frequent?

First, realizing that your reactions (usually an expression of anger) are resulting from stress and not from the behaviour of the other person.

Second, inserting a pause between your immediate reaction and your response allowing yourself time to moderate and change it.

Finally, recognizing that your reaction is an indicator of stress and then doing whatever it is that makes you less stressed. Exercise, vacation, reading, etc.

I interpret that as constructively figuring out ways to mitigate the stress point, instead of trying to ignore it or running from it, which is destructive, because it doesn't reduce or remove it.