Children who release unexpressed anger toward their parents by kicking the family pet illustrate the defense mechanism of

Displacement

Explanation:

Defense mechanism of displacement is defined as the mechanism in which negative feelings gets transferred from actual emotional source to other person or object .This is used by people for releasing and reducing their negative feeling caused through others. Negative repercussion chances decreases due to this mechanism.

According tote question, kicking family pet for releasing and reducing the anger caused because of parents is the way of displacement mechanism of displacement .  

can you give more details

answer; /// i believe its; // being treated lovingly and predictably by caregivers and learning to trust;