There's a former mental hospital 20 miles away that has a field of unmarked graves. Many prisons,including some in Britain and Ireland; many concentration camps, including some in South Africa; many prison camps, including some scattered across the Pacific -- and don't forget that even today in some areas of Europe bones are removed from a grave in a churchyard and the grave reused.

The bones of babies and children decompose faster than those of adult (soil, weather, etc. being equal). But everyone who has ever lived, is living, or will live will decompose and someone else will be buried in their dust.

Meménto, homo, quia pulvis es, et in púlverem revertéris.

Or to put it another way:

         Reincarnation
            Wallace Mcrae
   
    "What does Reincarnation mean?"
    A cowpoke asked his friend.
    His pal replied, "It happens when
    Yer life has reached its end.
    They comb yer hair, and warsh yer neck,
    And clean yer fingernails,
    And lay you in a padded box
    Away from life's travails."

    "The box and you goes in a hole,
    That's been dug into the ground.
    Reincarnation starts in when
    Yore planted 'neath a mound.
    Them clods melt down, just like yer box,
    And you who is inside.
    And then yore just beginnin' on
    Yer transformation ride."

    "In a while, the grass'll grow
    Upon yer rendered mound.
    Till some day on yer moldered grave
    A lonely flower is found.
    And say a hoss should wander by
    And graze upon this flower
    That once wuz you, but now's become
    Yer vegetative bower."

    "The posy that the hoss done ate
    Up, with his other feed,
    Makes bone, and fat, and muscle
    Essential to the steed,
    But some is left that he can't use
    And so it passes through,
    And finally lays upon the ground
    This thing, that once wuz you."

    "Then say, by chance, I wanders by
    And sees this upon the ground,
    And I ponders, and I wonders at,
    This object that I found.
    I thinks of reincarnation,
    Of life and death, and such,
    And come away concludin': 'Slim,
    You ain't changed, all that much.'"