http://revach.net/article.php?id=1535

Section: Halacha   Category: Tshuvos
Rav Shloime Volbe: Don't Hit Kids Above the Age of... 3
Rav Volbe writes in Sefer Zriah u'Binyan b'Chinuch that even though the Gemara says that it is forbidden to hit a kid who is over sixteen or according to another opinion 24 years old, according to the way things are in our times, he says, one who hits a kid that is only 3 years old transgresses li'Fnei Iver because the child, even at that age, will rebel against his father. 

Once upon a time it was possible to hit a child without destroying the relationship between the father and the child, nowadays it is no longer possible.  Hitting a child will always destroy the relationship between the parents and the child. The Sefer Minchas Shmuel says in the name of Rav Chaim Volozhin that harsh words do not penetrate or make any positive impact and a parent should only speak softly and with kindness. If in the times of  Rav Chaim Volozhin this was the case, certainly it is true in our times and even more so with regards to children.

Times have changed.  Rivka was suitable for marriage at age three.  Our kids are old enough to rebel at age three.

Important Note: We try to convey the Tshuva to the best of our ability. We admit that our understanding may not be accurate. Please also understand that this Tshuva may not be the final word on this topic. One should consult a Rav before drawing any conclusions.