If your nephew is travelling on a Singapore passport, he doesn't need a visa at all. He gets 15 days freebie visa-less in China. He'll probably get a regular entry stamp rather than the special transit stamp, and there shouldn't be any immigration supervisors checking onward tickets or other issues that other nationalities might have.

If the nephew is at least 17 years old, and has a goodly long connection time, he should definitely at least ride the maglev. He can tell his mother about it in a few years.