Yes.

Yes, of course they can. Think of it like this:

A child's ideology changes as they grow older due to new experiences and deeper understandings. Any person, adult or young, can change because no matter how old you are, you can still learn new things and go through new situations that can open your eyes to a new perspective. It's all part of maturing, that I don't really think ends until you're dead.

As well, if a person is evil, they most likely weren't born that way. Thus, this involves a changing process that would conclude that yes, a person can change. Whether that person can change back to "good" is the question, isn't it? I believe that can.