"On other hand do we really need to show innocent grade school students blacks in chains or slaves packed into wooden ships for the transatlantic transportation? Not to say it didn’t happen. How about Jews being exterminated in Nazi death camps. Does that need to be taught to a 10 year old just for the sake of truthfulness?"

Yes. We do.

"Not to gloss over the truth. Let’s use some good judgment to teach kids history and not make them afraid of being in the world or make them feel guilty for the sins of their very distant relatives. "

Not so distant. Most of us white folks had parents who disparaged people of color. How else do we teach the evils of racism than to point it out?