I came across a great kids addition to Firefox. Here is the link to Glubble's website where you can read more and download it. It is only available for Firefox, but you can download Firefox for free too.
Home | Glubble ®
You can customize it for each of the kids and adults in the house, giving everyone their own "secret homepage" that has the places they can go. There are groups of kid-friendly sites, organized by theme or topic called "glubbles" and you can pick and choose who is allowed to access each one and remove sites in the glubble you don't want. There is a "family wall" (kind of like Facebook) on each person homepage where they can post messages on the wall for the rest of the family to see. If the kids come across a site that hasn't been approved by you, they can easily send a request to you to add it with the click on a button.
Let me know what you guys think! I hope you like it!