Original Sin=Original evil?

So I got into a thread on a bulletin board because someone said "I don't think anyone would say babies were born evil."

And (thinking of original sin) went "actually, I know quite a few who would." And pointed out how children do not have to be TAUGHT to do bad things. But that it is natural, and up to parents to teach them out of it.

I DID point out that we don't punish babies for this because they don't know better. But did I mess up here? is sin NOT the same thing as evil? Because I've stirred up quite the controversy and now I'm second guessing myself. Bleagh.