Unless you have some type of paper trail connecting you to them, then technically you didn't watch their baby. No checks/contracts.
However having text messages and/or emails may be a bit problematic, but am not sure OP.
When they initially hired you & payment was discussed, did they actually mean "off the books" when they brought up payment??
Even though cash means cash (under the table), some people still do not get it.
If they said you would be paid that way, then did a switcheroo on you, they suck balls.
