>There is no way you can spin the argument such that the company would always derive higher profits by taking the moral choice.
No, because it's nearly impossible to get even two people to always agree what the moral choice even is.
But your examples are fairly easy: all of them are clearly net negatives for society, and would only be profitable for companies if they don't pay the true costs of their behavior.
Child labour carries a huge opportunity cost for the child: it can't get proper education, potentially costing it millions in lifetime earnings. Given a lack of immediate financial pressure, the economically rational decision for a child would be to demand far higher pay than an equally skilled adult because the salary has to offset the labor cost.
Similar arguments can be made for working people to death and giving them no vacation, but the payment schemes become complicated. Luckily they are even easier to solve: if unemployment is an acceptable condition (little stigma, decent unemployment benefits, etc), then the pool of people willing to work such jobs vanishes.
Of course regulation also works. Sometimes it's the sensible option (much easier to outlaw child labour than to teach economics and long term thinking to small children). But it is always valuable to first check if we can fix the root causes of a complex problem before we start with medicating the symptoms.