You can do this in the handler of the grid control's GroupRowExpansionChanging event. Don't forget to clear previously created child rows before you start adding child rows. The following sample shows how it may be done.

[C#]
private void unboundGridControl1_GroupRowExpansionChanging(
   object sender, Elegant.Grid.GroupRowEventArgs e)
{
   GroupRow groupRow = e.GroupRow;
   if(groupRow.Expanded)
      return;
   // Proceed only if the group row is expanding.

   groupRow.Rows.Clear();

   string time = DateTime.Now.ToString();

   groupRow.Rows.Add(unboundGridControl1.NewDataRow(new string[] {"1", time}));
   groupRow.Rows.Add(unboundGridControl1.NewDataRow(new string[] {"2", time}));
   groupRow.Rows.Add(unboundGridControl1.NewDataRow(new string[] {"3", time}));
   groupRow.Rows.Add(unboundGridControl1.NewDataRow(new string[] {"4", time}));
}

[VB.NET]
Private Sub unboundGridControl1_GroupRowExpansionChanging( _
      ByVal sender As Object, ByVal e As Elegant.Grid.GroupRowEventArgs)
   Dim groupRow As GroupRow = e.GroupRow
   If groupRow.Expanded Then
      Return
   End If
   ' Proceed only if the group row is expanding.

   groupRow.Rows.Clear()

   Dim time As String = DateTime.Now.ToString()

   groupRow.Rows.Add(unboundGridControl1.NewDataRow( _
      New String() {"1", time}))
   groupRow.Rows.Add(unboundGridControl1.NewDataRow( _
      New String() {"2", time}))
   groupRow.Rows.Add(unboundGridControl1.NewDataRow( _
      New String() {"3", time}))
   groupRow.Rows.Add(unboundGridControl1.NewDataRow( _
      New String() {"4", time}))
End Sub