is the arcade cashless as well? Can I set a specific amount on their sign and sail cards for them to spend?
I'm pretty sure (not certain) the arcade has a cash/coin machine that will exchange cash for tokens. Or, they can get tokens with their Sail & Sign card. The games only accept the tokens.
You can set a limit on their cards for the length of the cruise by setting up their individual folios with a cash deposit. Jim mentioned this as well. When they run out of money it will stop working. If you want to give them more you can by adding more cash to the account at the Info desk.
Jim, The Pursers can set up cash folios/accounts even if they are in the same cabin as far as I know.