You should be able to create a shortcut to launch the application from the new windows user account.
Once the account is created, click on start, then log off and select change user. From the windows log in screen, choose the new user name to log in to the user you just created. Right click on an empty spot on the desktop and choose "Create New... Shortcut." Navigate to the Virtual Families program application. It will be wherever you installed it, most likely on your C: drive in Program Files under the Virtual Families folder. When done, you should have a new shortcut to launch the game from your new windows user.
To give your son access to the families he had on your account you can copy the saved game files to the shared documents section, then move them to the LDW folder. I'll go over that process for you, but your statement that they are not on your user has me concerned. On the main windows user, when you open My Documents\LDW are the saved game files there?