Comment Unable to meet all requirements.... (Score 4, Insightful) 503
You want to keep the laptop secure. You want a 12 year old to use it. You want it to run Windows.
There is no solution. There will always be security risks and in some cases a negative time-frame to deal with them. Doesn't matter how good your AV is or what utilities you put on there, if it's connected to the Internet and there's a user at the keyboard then it is inherently insecure.
Now, how "secure" do you need it to be? If you're ok with putting that laptop on a separate subnet from everything else and teach the kiddo to do a proper update check every couple of days you should be able to mitigate most of the 'risk'.... but that seems a bit much to ask.