Who is older Merci or Judith?

Mercy is older than Judith.

"Mother has never told you much about our family, has she?" she went on. "You see, there was a boy their first child, two years older than I. I barely re- member him. We both caught some kind of fever. I got well, except for this leg, but he died."
"I didn't know," whispered Kit, stricken. "Poor Aunt Rachel!"
"There was another boy, after Judith," Mercy continued. "He lived only a week. Mother said it was the will of God, but sometimes I have wondered. He was very tiny, born early, but on the third day he had to be baptized.