Young children and those that have experienced early trauma require co-regulation before they can self regulate.  Co-regulation requires that the adult join with the child and bring them to a state of calm. This of course means that the adult must be calm. This is difficult because children can be so frustrating.  I observed a five year old and a father standing in line at a busy coffee shop. Of course the owner made the checkout line full of beautiful and tantalizing items. The father kept asking the child to stay out of trouble while he irritatingly waited in the long line. The child was left to regulate himself with an irritated and impatient father. As you might guess, the child continued to escalate as the father repeatedly corrected him.   A better solution might have been for the father to pull his son in, placing his arm around him in order to give him a sense of calm and containment.