I'm agree with 名花有主,Since their lives going to

have a big change after the school started, at least tell them what is going to happen, especially what kind of problems they will probably have at school. Tell them it will be normal for everybody(especially them) to take a while to get use to the new school life, try to be calm and have a positive attitude... If you already knew something was going to happen, even you could not change it -- face it,and try to be prepared as much as possible.