Ubuntu - Bottom panel not showing open applications

I gave my younger brother my laptop to use. Later I noticed that none of my open windows were showing on the bottom panel taskbar.

I'm guessing he deleted the applet that shows the open applications.

To resolve, I added the applet again by doing the following:

1. Right click on the bottom panel
2. Select 'Add to Panel'
3. Click on 'Window List'
4. Click on the 'Add' button.

Hope this helps.