During final days before my grand mother's death, she was able to recall her childhood memories, asking her sons to bring her brother. Before that, she had some kind of memory loss. Anyway, here, we need some sort of neurological explanation: Childhood memories stay in the lower part of the brain, as I read it somewhere (probably Oliver Sacks'); the neurological basis of many memory loss is on top layers of brain, that's why sometimes people recall vividly of their childhood memories, even playing piano despite with dementia.