Forsyth County authorities continue to investigate what caused twin 4-year-old boys to become ill Monday at their home.

The boys remained at Children's Healthcare of Atlanta at Egleston Wednesday.  One was in guarded condition, the other in stable condition, according to the Sheriff's Office.

"With everything they've done at the hospital, the doctors are just in a quandary," Sheriff Ted Paxton told the Forsyth Daily News. "They just cannot explain it."

Emergency personnel were called to a John Burruss Road home about 7:30 a.m. Monday after one of the boys became unresponsive.

While that boy was being taken to the hospital, the mother dropped off the other twin and a 2-year-old sibling at a babysitter's house, the Sheriff's Office said.

The sitter later called 911 to report that the other twin was in distress. He and the 2-year-old were taken to the hospital.

The 2-year-old does not appear to be sick, Paxton told the paper, adding the first boy taken to the hospital is in more serious condition.

A Sheriff's spokesman said there were no visible marks on either child.