Take a Deep Breath
Reflect on Your Gut Reaction
Give it a Minute
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I appreciate the attempt at honesty. This is an important practice for all parents to engage in.
While breathing exercises, pausing for reflection, etc., are interesting techniques to try to head off an anxious reaction as it happens, the next level down in self-reflection is to consider what decisions you're making before these moments even happen that you're feeling so overwhelmed by them in the first place. You actually hinted at this in your post, that perhaps you've over-scheduled and over-committed and its put you in a tense mood. Ironically, your temptation to react negatively toward your children who are not meeting your expectations may be a form of projection in that you are actually disappointed with yourself and not living up to your OWN expectations, ie, "What is wrong with you? Why can't you get done all this stuff you committed to and still be serene and in control?"
They are, after all, children, so it's extremely unlikely that anything they themselves are doing is the source of your reaction. Emotion comes from inside of us based on our own values and judgments. What expectations or judgments have you made of yourself that are potentially unreasonable and may be contributing to this dynamic?
Are you modeling for your children the kinds of commitments and expectations you think would be reasonable for them to live their own lives by?
Good luck!
The Lion - Well said.