Alright, I looked it up on my own. Here are some reasons people say we are born sinners.
Psalm 51:5 - Behold, I was shapen in iniquity; and in sin did my mother conceive me.
Psalm 58:3 - The wicked are estranged from the womb: they go astray as soon as they be born, speaking lies.
Ephesians 2:3 - Among whom also we all had our conversation in times past in the lusts of our flesh, fulfilling the desires of the flesh and of the mind; and were by nature the children of wrath, even as others.
Matthew 7:17 - Even so every good tree bringeth forth good fruit; but a corrupt tree bringeth forth evil fruit.
It is also said that we are born into sin because of the original sin of Adam and eve.