Laptop = bad idea.
My oldest daughter (she's 6) uses the desktop, which is in the family room. I have parental controls activated, and she only uses it for an hour at a time. The PC is situated so that we can see the screen from the couch or the kitchen. Giving her mobility is not wise, as she'll discover that the Internet connection goes with her anywhere in the house (if you have wireless). It's better to keep her locked on a static machine that you can monitor.
Also, don't let her use search engines. I have my daughter tell me what she wants (Dora, Disney, etc.) and I find it, access it for her, and add it to her bookmarks. That way, she doesn't feel the need to search for herself, and she gets used to having to run the content through me first.

