Vygotsky observed how higher mental functions developed through social interactions with significant people in a child's life, particularly parents, but also other adults.
As the candles on her birthday cake are lit and it is placed on the table, the child gains a feeling of deeply felt joy.
While these would be sufficient reason to arouse an emotional response in an ape, there are mental processes in a four-year-old that extend well beyond this.
A classroom, a game of soccer, a fire engine are all first and foremost cultural artifacts from which children derive meaning.
The history of the development of the higher mental functions is impossible without a study of their prehistory, their biological roots, and their organic disposition."
The sign mediates between the immediate sensory input and the child's response, and in so doing allows for a moment of reflection and self-regulation that would not otherwise be possible.
Even the birthday cake can be considered as a tool in that the parents use it to establish that their daughter is now older and has a new status in society.
It is from these simple inter-subjective beginnings that the world of meaning in the child mediated by tools and signs, including language, develops.