The guy had a friend over who started talking about ending the life of a bad guy who steals and punches people in the face. He brought this up independently of the guy, who also talks about death a lot. AFAIK, this friend is not exposed to any sort of real or fictional violence.
It seems all four-year-olds are Charles Bronson's who believe that all transgressors must pay the ultimate price, regardless of the extent of their crime. They also accuse each other of being bad guys a lot.