What is the deal with the "Slow Children at Play" sign?

Although "Slow: Children at Play" signs are posted in many neighborhoods, they're not approved for use by the Federal Highway Administration, which sets the national standards for traffic control signs. Traffic engineers tend to disapprove of the signs because they do not change drivers' behavior.

The National Cooperative Highway Research Program advises taking down "Slow: Children at Play" signs, believing that their proliferation encourages drivers simply to ignore traffic signs. In addition, traffic engineers express concern that the presence of the signs creates a false sense of security and sends a subtle message that it's okay for children to play in the street.