Well, one cause of flat head is baby spending too much time on their back, lying down, but there are many causes. Parents may feel guilty as they have left their baby lying on their back a lot and feel that they’ve caused it
My eldest had hip dysplasia so spent 12 weeks in a harness & on her back a lot. I was terrified of flat head but she didn’t get it. My youngest didn’t have hip dysplasia and had the weirdest shaped head as she insisted on lying with her head to one side when sleeping (so I had to keep switching her around her cot) but eventually it evened out.