There is no simple answer to the question of whether or not Pottermore is kid safe. While the website is not specifically geared towards children, it does contain a great deal of Harry Potter-related content that may be of interest to younger fans. In addition, the site includes some interactive features that could potentially be accessed by children.
That said, Pottermore does not appear to have any major safety concerns associated with it. The site has a privacy policy in place that covers how user data is collected and used, and it also uses encryption to protect user information. In addition, the site includes a number of security features, such as the ability to report inappropriate content. Overall, then, it seems that Pottermore is reasonably safe for children to use.