Manager Terry Collins offered his condolences to Harris and his wife, Trey, before Thursday's game at Detroit. Harris had gone on the paternity list Wednesday when his wife went into labor.
The Mets provided no other details on the death.
Harris played Tuesday night at Detroit and left the club during Wednesday night's win. Collins said it's possible Harris will rejoin the Mets on Friday when they return to New York for a series against the Yankees. It wasn't yet clear if his wife would be able to leave the hospital by then.