Question

A teacher taught the laws of washing the hands, etc., to his class, and said that if they forgot to bring a knife or salt and the like to the table, it is permitted to say to the members of the household, “knife,” “salt,” and the like, since these are needs of the meal.
 And he added on his own that if there is a child who is disturbing things and not allowing the meal to begin calmly, it is also permitted to scold him, for example, saying “rude kid” or “calm down,” in order to make the meal possible.
The parents complained.
The teacher argues that it is true this is not written in the books of Jewish law, but this is the reality in many more homes when trying to begin a meal.
 
Who is right?