15 After Nathan had gone home, the LORD struck the child that Uriah’s wife had borne to David, and he became ill.

Read 2 Samuel 12:15 Using Other Translations

And Nathan departed unto his house. And the LORD struck the child that Uriah's wife bare unto David, and it was very sick.
Then Nathan went to his house. And the LORD afflicted the child that Uriah's wife bore to David, and he became sick.
After Nathan returned to his home, the LORD sent a deadly illness to the child of David and Uriah’s wife.