For the next step, I'll give them a direct line to my bank account.
There's a new option for Switch buyers without credit cards, though you may need a few accounts.
Nintendo has added the option for payment via PayPal on the Switch eShop. The service allows for purchases online to be made without giving credit card information directly or even through a bank account.
Although the Switch offers multi-account support, the PayPal account must be set in the same region: a US PayPal account can buy items off the US eShop, but not the European or Japanese eShops.