Perhaps ostracism, abuse in kind, etc etc.
Of course, I'm not suggesting that I "sanction" the offending parents as the US sanctions Best Korea. That does nothing but starve the children/citizens being abused. Perhaps I place signs in my yard identifying the parents as abusers? Perhaps I place posters around town identifying the adults living at their address as abusers? Perhaps I tell anyone and everyone that those people are reprehensible? This is called "political pressure" and it'd do quite well at ostracizing an offensive party.
Should that not work, however, perhaps throwing pies at their car as they drive (without the children) or perhaps shouting insults at them will work?
Internationally this would include the removal of official recognition of the offending government as the sovereign representative of the nation. If they don't recognize the rights of their people, then they have no rights internationally themselves.