Final answer:
At 6 months, a child's brain is about 50% of its adult size, growing to 90% by age 6, with cognitive development characterized by 'blooming' and 'pruning' of neural connections.
Step-by-step explanation:
At 6 months of age, the brain is approximately 50% of its adult size. This rapid brain growth continues into early childhood, with significant growth in the frontal lobes, which are associated with functions like planning, reasoning, memory, and impulse control. By the age of 6, the brain reaches about 90% of its adult size. Cognitive and physical development is marked by periods of 'blooming' and 'pruning' of neural connections, leading to increased efficiency in brain function. This development, including myelination of neural pathways, continues into adolescence and is not fully complete until around 20 years of age.