Answer:
The process of neurogenesis begins in the fetal stage during pregnancy which continues until the adolescent stage.
The complexity of the neuron formation begins when the new pathways of the neurons are formed through synaptic junctions. The synaptic junctions allow the passage of impulse easily between the neurons and help carry out multiple functions.
Since the children's posses lower synaptic junctions than the adult, therefore, they are not able to operate very complex functions.