Making a PC safe for a 4 year-old

Not sure where to post this, but I suppose the MS Forum will do.

I'm looking for a good solution for safe web browsing.

Our daughter just turned 4 last month and she is naturally curious about the computer. About six months ago she figured out how to open Zune and scroll through to find the Tangled soundtrack and start playing it. A proud moment for both her and us as parents.

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via cliparts101.com

More recently, she has figured out how to open Chrome and go to the one website my wife lets her go to: pbskids.org. It's really easy to do because pbskids.org is pinned to the top 8 in Chrome. She has also figured out how to switch over to Chrome Apps where Angry Birds is!

Sometimes her curiosity turns out for the worse. One day I pulled up a video on YouTube for her and walked away. My daughter started clicking on video suggestions provided by YouTube, and before long, she was watching a Disney satire starring various profane, foul-mouthed Disney princesses.

On top of that, I've seen that she will click away on any warning or popup.

With all that background, any parents out there with a decent solution that will limit her exposure to age inappropriate content and protect us from viruses and malware?

Thanks