M.,
The human skull isnt actually one solid bone It is made up of three bones connected by cartlidge. When your daughter was born this cartlidge was verry soft so that the three bone making up her skull could squeez together as she went through the birth canal. The soft spot is where these three bones come together. As a person grows this cartlidge gets harder but is never as hard as bone. This allows the head to grow with the brain.
Just a small fact. When your baby is born you can touch the soft spot on their head. This cartlidge is fairly thick. So it's not like it is just skin protecting that small part of the brain.
I hope this was helpful.
B. P
Alittle about me: I am 22 yars old with a 19 mont hold daughter. I learned a lot about this kind of stuff when I was going to school for medical assisting. It didn't exactly work out since my daughter decided to come six weeks before she was due. It is nice when I can use the info. I learned for something. I guess it wasn't a complete waste.