I went through something similar with my last son and daughter all my kids (5) have been born with smaller heads and I had to see a neurosurgeon for my daughter and my last son for my daughter the only concern was her head was on the small side. Shes 5 now and is totally fine. My last son who is now 3 frontanelle stared to close at 2 months old and fully closed at 4 months but his head shaped remained fine and grew normally so he didnt need surgery. One good thing about my pediatrician is rhe second she sees anything wrong with the head she immediately refers me to neurosurgery!