With my third graders, we use the 3 R's (Readable, Relevant, Reliable) for determining whether a website is "just right" for them. I think a lot of librarians teach "just right" books, but finding appropriate websites is just as valuable.
For READABLE websites, I tell the kids to type the word "kids" as one of their search terms. This increases the likliehood of finding a website on their level.
For RELIABLE websites, I used to have students use Nettrekker, but we no longer have access. Now, I try to show them the kids version of IPL.org or how to use a subject directory like Kids Click, where you don't have to worry about reliability.
For RELEVANT websites, I teach the kids how to read the description in their results list to try to figure out whether that website is even worth opening. I also model changing search terms to find more relevant results.
After the mini-lesson, I give each child a bracelet, which I ask for them to keep in their desks until they go to the computer lab. The bracelet has three questions:
"Is is READABLE? Can I read and understand it?
Is it RELIABLE? Can I trust it?
Is it RELEVANT? Does it have what I need?"
This bracelet gives them Evaluating Power! By asking these three questions, they have the power to find the best websites available.