This is just a rumor so it needs to be confirmed by Sony officially.
According to a report from user garethager, Infamous: Second Son and Child of Light could be September's PS Plus free games.
He received a Playstation promoted post in his Facebook page and was able to take a screenshot. It seems it leaked a little early.
Infamous: Second son and Child of Light both received good reviews from the press and from the fans. An official announcement could be coming tomorrow. We'll have to wait and see.