Nurses wearing pro-Palestine insignia then told him he could not sit there any longer, and forced him onto the floor, Smus claimed.
The next time the family took their child to hospital he did not wear any outward sign of his Jewish identity and he was treated well, the sales director wrote.
The “proudly Jewish” boy is now “scared” to wear his kippah to hospital, Smus added.
A spokesperson for Manchester University NHS Foundation Trust said: "We are aware of images and very serious claims which are circulating on social media.
"We are rapidly investigating these to establish the situation and are discussing them with the family involved.
"Royal Manchester Children's Hospital is committed to providing high-quality care to all of our patients."
In a letter to the trust, Manchester Jewish leaders have expressed distress over the allegations.
“This is naturally hugely concerning that a Jewish family have been targeted due to the conflict in the Middle East. We are sure you will agree that it is imperative all patients are treated the same irrespective of their race or religion,” Marc Levy, the chief executive of the Jewish Representative Council of Greater Manchester wrote.
"This could have catastrophic repercussions for the Jewish community if they were to feel that they are not safe attending your hospital.”
The NHS trust must also clarify its position on staff wearing "political statements" on their uniform such as pro-Palestine insignia, he added.
Levy wrote: “Allowing NHS staff to wear these badges means many Jewish people seeking treatment at the Royal Manchester Children's Hospital and across the Manchester University NHS Foundation Trust will feel intimidated and unsure if they will receive equal and correct treatment. This is unacceptable.”
