Be sure to advise your credit card issuers and ATM card banks that son will be traveling in China during specific dates. I'd encourage the kid to pay by credit card when possible in nonsketchy establishments that accept one or more of his cards. IIRC this should generally include convenience stores, foreign stores, some chains, major transportation, most hotels (if applicable) that accept foreigners, and real restaurants, although less so in smaller towns or places that have fewer foreigners. Since ATMs sometimes don't work with foreign cards, he should try to keep a reasonable amount of local cash and perhaps also some larger clean crisp USA bills (maybe a couple $100s) to be exchanged into yuan at a bank/official foreign exchange place in an emergency.

BTW if he's going to China as part of some established program for foreign students, the program (or its USA partner) should provide advice on some of these issues, either in material sent out to accepted students or through links on its website. If he has access to a knowledgeable person at the program's (USA) headquarters, he can ask that person for advice about logistics of this nature. [It's part of the service you're purchasing.]