I noticed yesterday that one of my daughter's head is a bit flat on her right side because she favors that side. Her sister doesn't have it as bad, but she also have

My question is, how long before their heads harden up? I don't want it to be permanently flat on one side. So far, I roll up a little blanket and put it beside their heads to prevent them from turning to their right.

My 2 year old son always head his head turned completely to one side or the other when he was an infant, but he never got a flat head ... either that or I never noticed it.

My Advice:
Ok here goes,this is from experience and my own research,so make sure you all research and dont panic.

Plagiocephaly is a flatening of one side of the infants head usually found in twins and breach bubs. This ,due to the restricted room,causes the head to form slightly off symetry. Tends to start showing at about 8 weeks.

Brachiocephaly is a flatening of the whole back of the head, which makes the child look wide faced. Usually found in breach bubs. Again restricted room.

Twins especially at risk of neck problems where the ligament causes the head to favour one side.as lack of moment in the womb causes a tightening in the side least used. Hope this makes sense. These conditions are on the rise,due to babies sleeping on their backs. Rotation tends to work well for single non breech bubs. Twins and breech bubs should be checked out by pediactric physio or cranial osteopath before 12 weeks. They will loosen and streach the neck ligament slowly and gently and manipulate the cranial plates. No stress or pain to bub.

The cranium plates fuse at about two years and little can be done after this. However if rotation and physio fail, there is band therapy. Our daughter piglet was a breech bub and we were told by the Hospital and health visitor that the severe plagio and brachio would correct itself by 2yrs. Wrong. If no intervention then the child will have it for life. It was affecting our little ones eating and her face was starting to twist and her shoulders misaline. Our doc who had just returned from some time out , was horrified, she is Dutch, and despairs of the british system, even though she works in it. She put us in touch with a neuro surgeon friend and he looked at piglet and stated that she needed banding asap. Within a few days he had her in a private clinic in london and she was fitted with her Doc band. 23 hrs a day she wore it. Loved it, decorated it and slept really well in it for the first time. Four months later her face was no longer twisted and her shoulders were back in line. So do get your bubs checked by the physio and dont take no for an answer. If you can affoard it cranial oesteopaths are excellent with the condition. I would post photos but dont know how yet. We met a lot of twins at the clinic, because conventional attitudes had let them down. Our daughter still has a flat head and her ears are realy out of symetry, but since banding finished, not one person has mentioned her head shape. Prior to banding, people were constanty pointing out the funny shape of her head. Good luck to all parents and children with this problem mild or severe. Oh yes!Piglet is now 2 and five months and her face and shoulders are perfect now. All the best.