Here are some web sites that rate children's learning material.
Hope it helps!
Kerry gave one of the best sites which is SuperKids. Here are some more.
http://www.evalutech.sreb.org/otherorgs/index.asp (this is the best site that gives information leading to other sites)
http://mathforum.org/mathed/math.software.reviews.html (site that shows all the math review sites)