One of the most powerful things you can do to regulate your system is to use mindfulness to be aware of the moment and take some deep breaths. If you can recognize that you are in a red zone of negative feelings or better yet, you can recognize that you are approaching a red zone, that is the time to do something to regulate your system. If you are in a red zone, you have a much harder time thinking clearly and putting an event in perspective. You may have negative feelings, but if you are regulated, you can think clearly about what actions are going to best meet your needs.
My kids know all about deep breaths, but I usually have to be a bit creative about helping them take the deep breath. This is a great technique for breathing that I got from author and play therapist, Tracy Turner-Bumberry.
Touch the tips of your index finger and your thumb together and take breath in. Breath out slowly. Move your thumb to your middle finger and take another breath in and breath out slowly. Move to the next finger and the next finger doing the same thing. Then move back through the fingers doing slow mindful breathing. If you or your kids like a formula, this will well for you.
Also note, if you can make the exhale longer than the inhale and drop your shoulders (relaxed muscles) on the exhale it is going to be more effective in facilitating calm and regulation. When we are excited or agitated, we tend to take short breaths that are longer on the inhale. Your body does that to take in oxygen to prepare you to fight or run. So, to relax, you need to do the opposite, let out more breath, to relax your body.
Try it out and then teach it to your kids. If you have a family time where the family talks together, share with them what you learned, and tell them it is a tool to help them calm when they need it.
References: Turner-Bumberry, Tracy. (2019), 2 4,6, 8 This is How We Regulate! 75 Play Therapy Activities to Increase Mindfulness in Children. PESI Publishing & Media, Eau Claire, WI.