Final answer:
According to Freud's theory of growth and development, a child at 13 months putting everything in their mouth is in the oral stage, where the mouth is a major source of gratification.
Step-by-step explanation:
The behavior of a child at 13 months putting everything in their mouth is explained by Freud's theory of growth and development, specifically the oral stage. In this stage, pleasure is focused on the mouth, and activities such as eating and sucking play a significant part in a baby's first year of life. According to Freud, the mouth is a major source of gratification for a child during this period. A baby's inclination to put objects in their mouth lessens with proper weaning. Continued reliance on oral mechanisms for gratification in later life may indicate a fixation in this stage.