How many brain cells does a ten year-old have?
A newborn baby has all of the brain cells they'll have for the rest of their life, but it's the connections between these cells that really make the brain work. A child is born with 100 billion brain cells. A 10-year-old's brain may have stopped growing in size but it's nowhere near done developing.
Depends on a lot of biological factors based on genetics, any previous damage or genetic defect and other biological factors. You are born with roughly a 100 billion brain cells in a healthy brain, by ten your brain is it’s adult volume but neurons and links continue to change and grow.