Can I get an actual card for my son to use for his Apple Cash that I send him?

There is no physical card for Apple Cash.

Some things you can do with Apple Cash:

Transfer it to a bank account or debit card. See: https://support.apple.com/en-us/HT207882

Send it to someone: https://support.apple.com/en-us/HT207875

Use it to buy something where Apple Pay is accepted: https://support.apple.com/en-us/HT201239

Use it to make a payment on your Apple Card balance (if you have an Apple Card): https://support.apple.com/en-us/HT209226