Syrian Solidarity NZ posted to Facebook saying while the boy is in a stable condition, he does not know that both his father and brother have been killed. Their younger sister does not know either.
"Our hearts and prayers go out to this family and all the families affected by this atrocious act of terror that has certainly terrorised New Zealand as a whole," the post read.
Spokesman Ali Akil said Mustafa's wife and daughter, who were not at the mosque on Friday, were in "total shock, devastation and horror".