Do your babies have a soft bulge at the back of the head? I heard the soft spot at the back is supposed to harden by 1-2 months but my baby is 6 months old and it looks like it is bulging still.

If it is bulging, I would think that it would be good to check with the doctor. The soft spot at the back would usually close by 4 months. Soft spot usually look kind of flat or a little sunken. Perhaps you can check with your doctor at the next checkup.