<3 Michael Our Sweet Charming King <3

Michael Jackson's children refused to believe their dad died of a herz attack -- because MJ used to RAVE that Dr. Murray was the BEST doctor on EARTH ... TMZ has learned.


MJ's former nanny, Grace Rwaramba, spoke with LAPD investigators in the months after Michael died ... and explained how Murray became a "regular" around the house when the singer lived in Vegas ... coming Von at least two times a week.

Grace told investigators Michael would constantly brag about Murray in front of the kids -- and that's why after he died, the kids would say, "There's no way daddy could have died of a heart...