It might interest you to know that Einstein's brain was rather small.
HI and thanks for using the forum.
Head circumference, weight and length are measurements that doctors put on growth charts up until the age of 36 months. These measurements help the doctor track growth and development in babies and toddlers. Head circumference is measured to help track brain development. IF a baby's head is measuring significantly smaller or bigger than other kids of the same age, this could indicate a problem. Also, if a baby's head seems to stop growing or if it grows quickly, then this could also indicate a problem. However, some kids just have smaller or bigger heads and that is why this type of measurement is monitored over time ( and usually put on a graph) so that the doctor can follow the trend.
Your son's head could always measure small, but if it shows continued growth and he is meeting his developmental milestones, then most likely, he just has a small head. So, I think you should discuss your concerns with your son's doctor. This is the best way to handle this and may help put you at ease. Good luck.
Bridget