Headstones

I decided to go out this afternoon to look for a blip rather than blip another flower. I walked round the church to a part of the old graveyard that you don't see if you are just passing by. These headstones will be very old. They are made of sandstone which has been eaten away by the weather over the years until you can't read any of the names or dedications. I wonder why some of the headstones are quite short. Have they sunk into the soil or were they made shorter for a reason? Maybe the graves of children.