Everyone knows that babies have soft spot on the top of their heads. It's called the anterior fontanelle and you can think of it as a membrane window into the skull.It fills in after a couple of years but until that time doctors can actually conduct baby brain scans using an ultrasound!
Our younglings have these strange little soft spots because our ancient ancestors jumped through two evolutionary hoops around the same time: walking upright and increased brain mass. The bipedal shift required a major reconfiguration of the birth canal: It became narrower just as our stupid brains were becoming fatter.
As such, the skull's fontanelles make the skull more malleable, deforming and stretching the head's overall shape so that mom can push the creature free. The two frontal bones of the skull can even slide past each other to squeeze through!