var
  Settings: ITextSettings;
  Instance: TComponent;
  I: Integer;
begin
  for I := 0 to ChildrenCount - 1 do
  begin
    Instance := Children[I];
    if IInterface(Instance).QueryInterface(ITextSettings, Settings) = S_OK then
    begin
      // using ITextSettings methods and properties:
      //   TextSettings: TTextSettings,
      //   DefaultTextSettings,
      //   StyledSettings
      // to change properties of text objects
      Settings.TextSettings.BeginUpdate;
      try
        Settings.TextSettings.Font.Size := 18;
        if TStyledSetting.ssSize in Settings.StyledSettings then
          Settings.StyledSettings := Settings.StyledSettings - [TStyledSetting.ssSize]
            // show Font.Size := 18  
        else
          Settings.StyledSettings := Settings.StyledSettings + [TStyledSetting.ssSize];
            // restore showing Font.Size loaded from a style  
      finally
        Settings.TextSettings.EndUpdate;
      end;
    end;
  end;
end;