My daughter and I went on the Downtown Haunted History Walking Tour and it left us wanting to tag along on all their expeditions! I'm from Salem and learned so much about our local history and about some of the more gruesome aspects of our town that I hadn't known before. The Harris' were very knowledgeable of our town's darker and more interesting past and we got to use some of the same type of equipment you see on the "ghost hunting" shows on TV. I think the best part of the tour was watching my daughter get the scare of a lifetime (can't tell or it'll ruin it for some of you)!
Make sure to wear your walking shoes because it is a lot of sitting, standing, walking, etc. and I personally wouldn't recommend it for "little" kids but definitely early teens, teens, and adults with a natural curiosity and interest in the history you won't learn in school!