what substance aids the speed of a neuron transmission enabling toddlers to preform more complex tasks

Myelin

Explanation:

The myelin sheet is a layer of isolation that protects the neuron and it also increases the conductivity and cuts the time needed for the impulse to travel from one end of the cell to the other. It is made by 2 different cells in our body. In the CNS it is made by oligodendrocytes, and outside the CNS it is made by Schwann cells.