Toddler lumpy head

Patient: Hi I have a question about my twin toddlers. They are 18 month old and they have a lumpy head. I was wondering if it is normal, I never really paid much attention until my sister pointed it out. They are hard as if it is part of their skull. It does not bother them at all. I checked and i have similar lumps on my head, and so does my sister. could this be a family trait? They have a scheduled appointment next week so i will bring it up them, but i was hoping i could get some information right now. Thank You, Jennifer

Doctor: