If both parents live within the United Kingdom, child support claims are handled by the UK's Child Support Agency
The Court Service has information about magistrates' courts and county courts in the UK.
The European Judicial Network includes information about claiming maintenance in other member states of the European Union, and links to relevant authorities in those states.
The Australian Child Support Agency deals with international maintenance claims in Australia.
Child support in Canada is handled by the Canadian provinces, and the Canadian Department of Justice has information about the system there, including links to the various provincial websites.
Child support in the United States is handled on a state-by-state basis, overseen by the federal Office of Child Support Enforcement which has a useful page of links to individual state agencies.
Discussions about improving the global system of cross-border maintenance claims are under way at the Hague Conference on Private International Law and its website carries information about the work done so far by participating countries.