Final answer:
The best way to foster autonomy in a toddler is to encourage them to perform tasks by themselves whenever they are capable, which supports their sense of independence and self-esteem, aligning with Erikson's stages of psychosocial development.
Step-by-step explanation:
The intervention that will best foster the achievement of autonomy in the toddler is D. Encouraging the toddler to do things for self when capable of doing them. Autonomy in toddler development is a crucial stage characterized by toddlers wanting to exert their independence and accomplish tasks on their own, often verbalized as the "me do it" stage.
By encouraging toddlers to perform tasks they are capable of, they experience a sense of accomplishment and self-reliance, which is essential for their self-esteem and overall psychosocial development, as per Erikson's theory. While playing with other children and learning right from wrong are also important, they do not specifically target the development of autonomy as strongly as allowing the child to do things by themselves.