No. A flat head (plagiocephaly) does not affect development, and the flatness will go away as your baby spends more time on his tummy when awake and begins to roll, crawl and move. However, a baby who has developmental problems is more likely to have a persistent flat head since he is not moving around as he should.
No. There will be no developmental problems however you would be advised to have your baby sleep on alternate sides on alternate nights to minimize the cosmetic results. If that doesn't work, or the problem is severe, your child might need to wear a helmet to correct the end result. Depending on where the flatness is, your pediatrician might be concerned about premature closure of the skull sutures.