Final answer:
A three-month-old child sucking on his thumb developed this pleasure from the sucking reflex, which is part of Piaget's sensorimotor stage and Freud's oral stage of development.
Step-by-step explanation:
Laurentis, a three-month-old child who finds pleasure in sucking on his thumb, likely developed this behavior due to an innate reflex known as the sucking reflex, according to Jean Piaget's stages of cognitive development, specifically the sensorimotor stage. At this stage, from birth through age 2, a child explores the world through senses and motor behavior. Furthermore, Sigmund Freud would attribute this behavior to the oral stage of psychosexual development, where the main source of pleasure and soothing for a baby is through oral activities like sucking.