[Problem is, Obi-Wan didn't know either. He could only speculate.]

The Dark Side and those that use it are everything the Jedi are not.

A focus on self, hate, anger, and using it to make one stronger. A child who does not feel secure in himself, as many tend to do, could easily fall for these deceptions without proper guidance. Watch for signs of this, anything that would be out of the usual for him.

I distinctly remember the first time Anakin talked back to me. He hadn't before, at least not like that.