If your child can read the Harry Potter books (SS/PS-HBP), this site is fine. The problem with it is that Jo almost never updates it. It's a good site, and a fun one, but don't expect anything new. It hasn't been update since Half-Blood Prince came out.
This website keeps you in touch with harry potter as well as j.k. rowlings. It is also fun and interactive and has some personal things such as drafts and pictures before published as final copies.
I love this website, and anyone who loves Harry Potter will love it too. With JK Rowlings autobiography, Rumours [hysterical!], and the Other Harry Potters, I will always return to that website again and again!