"We do not remember days,
we remember moments."
~ Cesare Pavese, Italian poet & author (1908 - 1950)
It is only of late that I am observing that children naturally live in the moment. I am not a psychologist but it appears that children are not distracted by cumbersome past and future thoughts. Yank them from their immediate activity and one quickly learns how important the moment is to them! They will protest.
Living in the moment is a skill that adults may be able to relearn with practice. I am working on it.