Final answer:
Vygotsky referred to "private speech" as the phenomenon of children talking to themselves aloud, a crucial part of their cognitive development and self-regulation according to his socio-cultural theory.
Step-by-step explanation:
When Vygotsky characterized young children, by the term "private speech" he was referring to B) Talking to oneself aloud. Private speech is a self-directed speech that children use to guide their own actions and thoughts, often used during problem-solving or when they are trying to understand something new. It is a part of Vygotsky's socio-cultural theory of cognitive development, which emphasizes the importance of social interaction and language in learning.
Vygotsky saw private speech as a means for children to plan, regulate, and control their behaviors, which eventually becomes internalized as silent inner speech. This process exemplifies how children transition from social speech (language used with others) to internalized self-regulation and cognitive development.