Take slow, deep breaths, inhale through the nose and let the belly expand, then exhale through the mouth.
Imagining holding a flower, kids can inhale the flower's sweet scent, then slowly exhale, "blowing out" the petals.
Like the breaths of a bunny, this exercise has children take three rapid sniffs through the nose, then one long exhale.
Breathing in different colors, associating each with a positive emotion or quality, like breathing in "calm blue" or "happy yellow."
Simply having kids count each inhalation and exhalation, up to a certain number, ask them to stay present and redirect focus.