Notice that all of the three top row pictures of POTUS Barry at the same approximate age as Baby David Obama show much less hair than Baby David.
My wife, the neonatal nurse, would frequently remark on how some babies are born with a full head of hair (black or South Asian babies) while others don't have significant hair come in until age 2 (more often Caucasian babies)!Brothers David and Barry differ in respect to their first-time hair growth.
Your picture display shows David with lots of thick hair at approximately age 1.5-2, while the POTUS Barry baby pics at that same age show very little hair in the first growth.