Final answer:
By the time a child is 10 years old, their brain is approximately 95% of its adult size, with most of the size increase already occurring by the age of 6.
Step-by-step explanation:
By the age of 6, the brain has already reached about 90% of its adult size. The rapid growth phase of the brain, known as 'blooming,' happens during the first few years of life, leading to the formation of numerous neural connections. This developmental stage is crucial as it lays the foundation for cognitive abilities like planning, reasoning, memory, and impulse control. As children grow, specifically around 10 years old, their brains do not increase much in size but rather in complexity, with significant changes such as synaptic pruning and myelination making the brain more efficient. Therefore, at 10 years old the brain is about 95% of its adult size.