1. First launch Windows’ task manager. In Windows XP you can do this by pressing CTRL, ALT and DEL key simultaneously. In Windows 7, it is normally done by clicking on the task bar and then selecting "start task manager”, but since your task bar is not there in this case, let’s press CTRL, ALT and DEL keys simultaneously here as well and then click "start task manager” from the menu.
2. The task manager would look something like image 1 below. Click on the Processes tab as shown in yellow, if you are not already there by default. Here you will see many processes running. Select the process named "explorer.exe” and then hit "end process”.
3.Then go to the file menu on the task manager at the top left corner and choose new task
4. Another command window will pop up as shown in fig 3. Type "explorer” in the command line and hit OK. It will do a fresh restart of your Windows explorer in default mode.
As soon as you have run the above command, your Windows taskbar will be restored exactly at the position and size it was before getting disappeared. It makes sense however, not to show the kids this entire process of ending and restarting tasks in the task manager – you may find yourself fixing more complex issues than this!