SOS
Breathe first. Then speak.
Say it in the voice of:
What to say right now · Emotion Coaching
"I'm sorry I yelled. My frustration got really big and came out loud. That wasn't your fault—my job is to keep my voice calm even when I'm mad. I love you, always."
Your body first
Put one hand on your chest. Breathe in for 4 seconds, out for 6. Even in close, secure families, parents and children are out of sync much of the time. Coming back together is what protects the relationship, and you can do that right now.
Afterwards
Offer a warm physical reconnect (hug, high-five, or sitting nearby), then restate the original boundary calmly.
Avoid
Never add a 'but you...' to an apology ('I'm sorry I yelled, BUT you weren't listening'). Own your nervous system 100%, then hold the boundary calmly.
If you're afraid you might hurt yourself or your child, put your child somewhere safe and call or text 988 (US). Outside the US, call your local emergency number.