For a safer experience on the computer for your kids, & a more secure unit for you, try making a separate 'limited user' account for the kids. (Control Panel> User Accounts> Create an Account; Limited)
On that they can have their own wallpaper & screensaver, 'My Pictures' folder of just their photo's, desktop icons for specific kid oriented applications, and so on. This can omit a lot of aggravation for them, & you don't have to constantly assist them find things.
You (administrator) can install 'parental controls' to take out some of the risk of random website viewing, and for the really younger ones, dedicated browsers just for kids can be used for sites specific to juveniles.
Added benefits are much greater security (virus threats, undesirable applications, and peer-2-peer files sharing can be drastically curtailed).
Parental guardian applications allow the admin. (parent) control over: specific sites allowed or not allowed; time of day use; site barriers for language, nudity, violence, and more.
Read the reviews & user comments for several applications listed, to see if any match your needs, and skill level.
http://www.snapfiles.com/Freeware/misctools/fwparents.html
"Toddler Keys"
is a useful tool for parents that allows you to lock your computer keyboard, CD drive doors and power-off button. When the keyboard is used it will display images and play sounds every time a key is pressed, thereby preventing access to the desktop and applications, while adding some entertainment value for the kid. You can select the images and sounds to be used by copying them to the Toddler Keys folder.
http://www.snapfiles.com/Freeware/system/fwutilities.html
"KidRocket"
is a web browser for kids, that limits Internet access to about a dozen child-safe websites (Sesamestreet, Crayola, Nick and others). It offers a full-screen interface that can be locked by the parent, effectively preventing access to the desktop or other programs while it is running. In addition to web browsing, it also includes a doodle pad, a virtual Starbrite game and a math trainer. You can also choose to disable printing and keep track of the time the browser has been in use.
http://www.snapfiles.com/Freeware/misctools/fwbrowser.html