Silas went to the Red House to get a doctor for the woman and baby he found.
In chapter 13, Silas discovers Molly and her baby. He goes to the Red House to find a doctor, because Molly is dying. There is a New Year’s party going on, and the guests are very curious about the sick lady and her beautiful baby daughter.
“It's a woman,” said Silas, speaking low, and half-breathlessly, just as Godfrey came up. “She's dead, I think—dead in the snow at the Stone-pits—not far from my door.” (ch 13)
This is how Silas ends up with his “treasure,” Godfrey and Molly’s baby daughter. No one expects the old hermit to want to keep a baby, but Silas seems to take well to parenting. He raises the girl as his own, and loves her more than anything. Since Godfrey would rather have nothing to do with her, he prefers the arrangement.