My friends baby is four months old.... While she turning... her head will fall..wat is the reason???

A. Hello ma’am Mostly by the age of four months maximum a child’s head is stable so if your child’s head is still not stable or your friends child’s head is still not stable as per the age then I was simply advise you to consult your paediatrician ones for a proper checkup and medication or any other treatment the doctor has to advise you