All I can remember is that a couple's daughter/son goes missing. They are talking to the police I think and they are told that their child may have passed a sign that said quick sand.
Fast-forward to years later when the parents are old. They get a knock at the door and it is their missing child, but he/she has not aged at all. I think the little girl/boy came back to take the mother to heaven.
I thought it was a Twilight Zone episode or the Outer Limits, but I have searched all episodes of both and I cannot remember what this show was. Does anyone know?