Just as Laura walks around and prays for the children in other nearby graves, she trusts that other people will see her children and keep caring for them.
This is why praying for the living and the dead is a work of mercy. It's good for the souls of those we are praying for, it's good for our own souls, but it's also this quiet, unknown act of charity to loved ones and neighbors who will pass by and know you were helping out their family while they were away.