Thank you for all the answers. The teachers and assistants said because the children most of the time are not listening and obeying that's why they have to yelled at the children so they will listen. I understand that some children are not easy to sit still and listen (they are 2 and 3 years), but I disagree that preschool children should be treated like that. What happened at home after? I think I will take nanny at home so I can monitor my twins better.