Cultural transmission

How do the members of a social group pass on the accumulated knowledge over time? How does a toddler learn from the members of their community? By being able to represent social categories, we can also find out who shares our own cultural knowledge, patterns of behavior in our own culture with us, thus inferring to what extent our knowledge of the world may be overlapping. For example, babies prefer to learn from a person who can convey culturally relevant and useful knowledge so they can become a "full" member of their culture. What other factors help babies so early to learn so much from the world and culture around them?