nana - He need not talk just to his bank for credit card processing services. Banks traditionally charge higher interchange fees than other processors and ask for much longer contracts. Some idiot at Fifth Third once offered me a lower processing rate for one year than anybody else, but a FIFTEEN YEAR contract. In other words, the first year was a teaser rate. Shop around. There are many other processors interested in capturing small business card processing. Even Costco offers it's business members credit card processing and its highly competitive. He does not need to get any permission from his bank to use an outside processor linked to his checking account.
The link below is just an example of one of the hundreds of possible credit card processors your son could get a quote from. (I never used this company - this is not a recommendation.)
Another important issue is equipment. Rent, lease with a buy out or buy outright? He will have to make that decision. All have pluses or minuses. If he buys the equipment make certain that it is a major brand that can be used by any other processing company. Otherwise he'll be stuck with useless equipment should he decide to change companies.
With all companys watch for the fine print. Especially contract renewel periods. Some automatically renew for long periods (years) and give you a very narrow window to end your contract if you're dissatisfied for any reason. Some charge punitively high cancellation fees.
The bottom line is this: He needs to know the profit margin on every single item he sells to determine if the profit margin is lower than the credit card processing fees. Those items he will be selling at a loss. It wont matter how many more sales he makes by accepting credit cards. He could still lose money.
In the C-Store business, which has razor thin margins, many small sales were net losses when a debit/credit card was the form of payment.