Theodisk, you obviously didn't have many children or many siblings. You would notice right away how different kids can be from the moment of birth. They could grow up in same environment, same parents, same teachers, same water, food, air, family. At the end of the day you you'll have different people with different interests, personalities and talents.
Interestingly the differences are bigger when parents are of contrasting personalities, intellect, etc.
On other hand go to Amish or hutterites closed colonies and you see how similar people in colony are. They mingled long time together in these closed communities, and you'll have almost same mold, DNA.
Observe little newborn kids, or early weeks, and you'll see immediately differences in personalities, characters, physical development, motor control and coordination, attention and interests what they love to watch or listen .
No, we are not born same, clean slate.