Final answer:
Infants' understanding of their behaviors' effects and trial and error learning are part of Piaget's Sensorimotor Stage of Cognitive Development, the first stage in his theory.
Step-by-step explanation:
The process of development where infants learn to understand how their behaviors affect the world and engage in trial and error actions is described in Jean Piaget's Sensorimotor Stage of Development. This stage is the first stage in Piaget's theory of cognitive development, which lasts from birth through about 2 years of age. During the sensorimotor stage, a child absorbs knowledge of the world through their senses and motor behaviors, eventually developing crucial cognitive skills such as object permanence.