On DogEared kids can write and post their own book reviews. I don't know for sure if children are actually interested in reading one another's reviews but I have to say that as an adult I love them. These young reviewers – unlike so many adults – don't waste any words. They tell you what they think, right up front and center, and oh boy is that refreshing.
The site also recommends books and I was pleased to see some old favorites (like "A Cricket in Times Square" by George Selden) as well as to discover some new ones ("Shakespeare's Secret" by Elise Broach and "Tuck Everlasting" by Natalie Babbitt.)
National Geographic maintains a number of blogs for kids, all of which make good reading for children and adults alike.
In fact, if you're looking to feel a little bit better about the world today, just take a look at the National Geographic blog that offers four stores about animal kindness. At least I know that my morning is looking brighter since I read read about the shy young chimp who gathered up his courage to climb down a tree to offer a snack to a hungry human.