Parents need to know that because many of history's mysteries involve issues related to war, violence, and other less-than-happy subjects, some of the scenes in this series might be disturbing for sensitive or younger viewers. That said, the re-enactments themselves aren't particularly graphic, and most tweens should be able to handle them. More troubling is a lack of logic parading as evidence and proof. Younger viewers without much experience of history might be misled into accepting as fact something that is, at best, conjecture.
Positive messages:The narration tends to be contradictory -- even as it proclaims that contradictory eyewitness accounts are proof that the accounts have no substance. The show also draws questionable conclusions from very flimsy evidence. In short, it seems to encourage innuendo and conspiracy theory. That said, it also looks to scientific evidence for proof and uses some good scientific process to analyze that evidence.
Positive role models:While there are scientists involved in digging up (sometimes literally) the answers to these historical mysteries, there are also a lot of conspiracy theorists without strong academic backgrounds.
Violence:Since many of history's questions involve people dying, war, and other conflicts/issues, there are scenes related to blood and suicide. For example, in one episode involving a potential suicide, pictures of the bodies are shown, along with close ups of a gun about to be fired into the person's mouth -- but you don't see the mouth or the gun firing.
Having seen the episode on the "haunting" at Wolf Manor in Clovis, CA, I'm completely unimpressed. They indeed tend to go into these investigations with a preconceived notion. One thing that really undermined this show was their continued assertion that the Amityville haunting was a fact when, in actuality, it has long since been debunked as an elaborate hoax. Come on, History Channel, give us some credit!