When Jessica was 3 and 4, and she got really upset from crying, I would tell her to stop crying and calm down. She would say she couldn't. So we went through this routine where I would tell her I'd breathe with her on the count of 3: "1, 2, 3, breathe!" and we would both suck in deep breaths. After repeating this a few times, she was usually calmer.
I don't remember doing this recently, but I must have because Xander picked up on it. He'll be crying a little, sometimes even fake crying, nothing like Jessica had done when I helped her breathe. Even though he's not crying that hard, he'll say, "I need someone to help me breathe!"
So I go through the routine with him and after one try, he's calmed down from his not-so-agitated state.