GOODNESS! I have a hard time recalling a post with so many inaccurate assertions in a long time.
Spiritually, I would agree that children do not technically sin until they reach some age of accountability. HOWEVER, I've observed rebellion and defiance in infants. I think most parents with any fair-mindedness about it at all would agree. Certainly by 2 years such things are VERY EVIDENT.
And, we also have the sins of the fathers visited upon children to the 3rd and 4th generation as Scripture makes clear. So I find the point greatly moot, AT BEST.
Do personalities evolve? Not greatly. There's some refinement, mellowing . . . but the basic personality structure does not change much birth to death--especially for most people.
Are some children born with criminal traits? Some experts would say yes; some no. I think the most Biblical perspective is yes, some are. And, there's some science to back it up. It gets very complicated and I don't care to dig it all out.
Children are born with a sinful nature, therefore they are sinful even if they don't exhibit it until they get older. They are innocent until such time perhaps but they are sinful because of being born with a sinful nature.