Funnily enough, the Criminal Code of Canada actually authorizes parents, teachers and other guardians to use physical force or discipline to punish a child under their care. It is subject to a test of what's reasonable under the circumstances.
Domestic violence, by definition violence in the home, is self-evidently harmful with respect to partners. Why does it seem to be a persistent issue to apply that same approach when it comes to corporal punishment of children in the domestic situation?