I hope OP is ok and already found another, much better family.
I would dare to say that probably already are looking for another aupair since who else would let their child deliberately hurt their nanny...?!
Although I hope the OP is okay and finds a nice new post, I still think that talking to the parents again and letting them know how insupportable the sitation is, there is a possibility things may change.
As per her posts, she has already discussed this thing with them and got an answer. If I got this answer I would move to a dif job, quickly. But I agree, sure, parents need to be advised so the next poor girl can be spared some inappropriate kid behavior.
Children don't feel safe with someone they can abuse.
It would be interesting to know if and how many au pairs they have had
I wonder if the OP solved her situation or if she found another job.