Facebook, or any other social networking sight for that matter, can create problems for organizations that care for children. The neat thing about Facebook is sharing pictures with people - some you know and some you don't. And from the Facebook pages I've visited, many like to capture pictures of their regular activities, so when you work with children, it's logical that you'd post pictures of you and the kids you take care of.
In many cases, before any photograph can be published or distributed publicly, unless it's a large group photo, the individuals pictured need to sign a consent form authorizing the distribution. I think Facebook and other social networking sites get too close to that line of demarcation. One can argue that Facebook isn't a public distribution of a photo. We need to place ourselves in the shoes of the parents.
So while I won't state that it's definitively a problem, it's too close for comfort for my take on the matter. I think paid and volunteer staff should be trained that they need to be highly protective of the pictures they take while serving/caring for children, if they take pictures at all.