Jewish schools are on high alert after a bus load of Jewish children was bombarded by five teenagers screaming "Heil Hitler" and "kill the Jews" in Sydney on Wednesday.

Five teenagers have been arrested after they boarded the school bus and terrorised students as young as five while the vehicle travelled between Randwick and Bondi Junction, police said.

Mount Scopus Memorial College principal Rabbi James Kennard asked all school bus drivers to review their security requirements and procedures in the event of an emergency..

Principals of The King David School (KDS) and Leibler Yavneh College have told parents in letters and emails they were consulting with

authorities and taking precautions to protect students and staff.

In his letter to parents, Yavneh College principal Roy Steinman wrote that he had concerns there would be a negative response from "some sectors" of society to reports that two former students had been wounded while fighting for the Israeli Defence Force (IDF) in Gaza.