That they have the right to feel safe at school.
That they do not have to suck up any anti-semitic 'banter'.
That it is the teacher's job to address bullying - anti-semitism is bullying.
That they are not responsible for Israel's actions.
That they do not have to explain or justify anything about Israel or Jews.
That it is the teacher's job to teach about Judaism, Israel and anti-semitism, not theirs. They are the child being educated, they are not the teacher.
If they feel confident speaking up, then fine, they can go ahead. But if they do not want to speak and be the Jewish figurehead or educator, that is also a fine choice.
But to be supported in these rights and choices they have to report it. To their teacher and to you so that you can back them up.