retrieve data from db and display in gridview c# then insert

Question

I am Retrieving data from two table into webform,in which gridview and Textbox ,then again i am trying to inserting data into same table with new ID ,but data is inserting into Master Table ,but not getting insert into Child Table

Here is my Retrieving query

if (txtRefno.Text == "") {
 Response.Write("<!-- Inject Script Filtered -->");
} else {

 using(SqlCommand cmd = new SqlCommand("[Sp_BalPakinsert]", con)) {
  cmd.CommandType = CommandType.StoredProcedure;

  cmd.Parameters.AddWithValue("@Order_Ref_No", txtRefno.Text);

  cmd.Parameters.AddWithValue("@OrderNo", txtOrder.Text);

  con.Open();
  PID = Convert.ToInt32(cmd.ExecuteScalar());
  con.Close();

  DataTable dt = (DataTable) ViewState["dt"];
  int codeitem, qty, orderno, prdno;

  foreach(DataRow row in dt.Rows)

  {

   //pid = int.Parse(row["_PID"].ToString());
   prdno = int.Parse(row["Prdno"].ToString());
   orderno = int.Parse(row["Orderno"].ToString());
   qty = int.Parse(row["QTY"].ToString());
   codeitem = int.Parse(row["Codeitem"].ToString());

   this.InsertRows(codeitem, qty, orderno, prdno);
  }
 }
}
}

private void InsertRows(int codeitem, int qty, int orderno, int prdno) {
 con.Open();
 using(SqlCommand cmd = new SqlCommand("[SP_BalPakDetail_Insert]", con)) {

  cmd.CommandType = CommandType.StoredProcedure;

  // cmd.Parameters.AddWithValue("@PDID", _PID);
  cmd.Parameters.AddWithValue("@PID", PID);
  cmd.Parameters.AddWithValue("@CodeItem", codeitem);
  cmd.Parameters.AddWithValue("@QTY", qty);
  cmd.Parameters.AddWithValue("@Orderno", orderno);
  cmd.Parameters.AddWithValue("@Prdno", prdno);

  cmd.ExecuteNonQuery();

  con.Close();
 }
}
public object PID {
 get;
 set;
}
}

}