My favorite go-to activity to help our little ones with regulation is Bubble Mountain. All you need is water, a straw, a container and a few pumps of dish washing soap.
I suggest placing the container on the floor and having children lie on their stomachs, resting on their elbow and forearms. This position stabilizes the upper trunk, which discourages upper trunk breathing. Movement in the belly is desired. Movement at the shoulder and collarbone is inefficient and fatiguing.
Just a few minutes of blowing can reset a child’s arousal state. Children of all ages love this activity.
Another great tool are soundless pipe whistles. Most whistles are loud, shrill and alerting. The soundless whistles are fun and calming.
Below is a fun Elmo video song called “Belly Breathe”. Watch it with your little one and try modelling diaphragmatic (aka “belly breathing”) breathing next time your child has a high arousal state.