Spanking in Canada
This article may explain why some people are generally wary of having the United States sign on to international treaties that could then be used to overrule state and local laws:
In October, a United Nations committee ruled that Canadian law violates the U.N. Convention on the Rights of the Child, and that Canada should 'prohibit all forms of violence against children, however light.' The committee specifically called for abolishing Section 43 [which allows "reasonable" use of spanking by parents].
But if the Supreme Court does strike down the section, a lot of parents are in for a surprise. Spanking would be no different in law from any other common assault, a criminal act punishable by imprisonment for up to five years.