Will I be legally liable if a child becomes infected and dies, or will
that fall to the proprietor who knew?
Both you and the proprietor would have legal liability, probably for punitive damages as well as compensatory damages, because you knew about the clear and present danger of making other people sick, or even causing their deaths, and you did nothing about it.
Your liability isn't even a close call, because, as noted in the answer by @user6726 there is regulation that you were or should have been given notice of which specifically prohibits you from working in this situation.
Also, even if you have few symptoms, that doesn't mean that you aren't still contagious, as you acknowledge in your question.
You and the proprietor would each also probably face criminal charges of negligent homicide or manslaughter. Each of you would be guilty of those crimes.
Missing pay is not an option I can afford unfortunately; the moral
implication of my working is out of my control.
This is bullshit.
You are culpable and you are capable of not doing work you are legally not allowed to do. If you have to quit and find another job, then that is what you must do. If that means you need to apply for unemployment benefits or welfare, then that is what you need to do.
Millions of dollars of legal liability that can't be discharged in bankruptcy because you caused it willfully, and years in prison, are what shouldn't be an option for you.