For a while, we had different login for DD4 when she started using the computer at 2. We had our own login to get into windows and then she knew to pick her icon to get into her desktop. DH did this to control what she could get into and to ensure she didn't do anything damaging to our desktop. Google has a system for kids called Glubble that lets you control where they go, although we didn't use it for a real long time.
There's also a cool, free program called Tux Paint that DD LOVES.
Other good sites: starfall and poissonrouge
We have never set limits on DD's computer use and have had no problems. After a while, the novelty wears off and although your DD will probably always be interested in the computer and the web, her intense interest will probably wane a bit as time goes on.
