"Corporal punishment is allowed, as long as it's done in a 'dignified' manner, pontiff [Pope Francis] says. Do it justly and move on, he says." - Deborah Hastings, New York Daily News, February 6, 2015. Here is the article.
Perhaps it is the clash of cultures: European values about child-rearing versus American ones. But, Pope Francis will have a battle on his hands justifying to Americans, both Roman Catholics and non-Catholics, that hitting a child is permissible.
The movement against spanking has reached the point that such activity is viewed as a type of illicit erotic pleasure. Therefore, it's inappropriate to conduct with a child. Part of stimulating sexual pleasure among some is inflicting physical "punishment."
As a thought leader Pope Francis may become ineffective. That's because he pontificates, literally, on so many issues. He might give himself a longer shelf life if he restricted himself to one issue such as peace - among people and within oneself.