Try www.kidrex.org It is basically Google but is supposed to be filtered to a greater extent.
I teach in China and I have all ESL students so I made a list of web search resources for my students. They are listed on my website for my students; www.apriln1988.weebly.com Feel free to check it out... or use it. It is a beginner's level website as I am not a web designer, so have patience! I'm working on it ;)
WorldBook Kids is a great source for students to use when researching. My school district subscribes to this site. Check with your school's librarian for other resources that are available in your district.