Hi mommy! Yung flat head, nangyayari pag laging nakasandal si baby sa isang surface, like a carrier or a seat. Dapat may regular tummy time siya para maging round ang head niya. This article might help you: https://ph.theasianparent.com/tummy-time-baby-spine-development/
My mom's practice when we were still babies, pinapapalit palit niya kung saan naka side si baby. Hindi yung naka flat lang all the time, minsan right then left naman para balance.