At one time or another everyone's temper flares releasing tension, frustration and anger. Children can be their own worst enemies. They have strong desires, limited abilities, and difficulty managing their emotions. After numerous unsuccessful attempts to tie her own shoes, a frustrated 2 year old throws her shoes and kicks her feet. Temporarily losing sight of her capabilities, her temper takes over.
Tantrums are one way of expressing anger.
In the grocery store the little boy quickly learned that his actions were not working. Trying to reason with a kicking, screaming child is usually ineffective and frustrating, in itself. So sometimes the best approach is ignoring the tantrum or isolating yourself or the child from the situation. It is no fun to have a tantrum alone. A successful tantrum results in a power struggle.