I could not find either child in "Cemetery Inscriptions of Highland County, Ohio" (1954) by David and Jane McBride. This was a rather complete reading of headstones found in graveyards, family plots, etc. Many were dug out of the ground in forgotten places. If they did not find a stone it likely does not exist.

The 1860 census for Hamer Twp. shows:
LUDWICK
Robert, 29, farmer, Va.
Amanda, 20, Ohio
Frank, 2, Ohio

If Amanda was indeed only 20, she would have been very young to have 3 births already. Not impossible, though. I could not a marriage record for this couple in Highland County.

good luck,
Steve