A child becomes anxious when they have to leave their pre-schooling environment behind and join the junior sections of a senior-secondary school. Friends change , teachers change , the surroundings change and so do the curriculum. They would now get the real taste of real academic life, of maths , Literature , Social Science etc.
It is quite normal for the kids to feel worried. They would be leaving behind their carefree lives , their playmates, their teacher and enter into a world about which they are unaware of.
Parents can have a talk with them in order to calm them down. They can reassure them by saying that they would be able to make new friends over there and they would enjoy themselves over there. In order to prepare them for the transition, parents would now have to pay attention to their academics- by introduction of tougher topics like rhymes, sentences, arithmetic operations so that they do not get overburdened by the curriculum of the new school.
They must train their kids to follow the basic norms- like asking permission to have water, food or for going to toilet. They should also install proper potty training in them so that they do not end up excreting in the classroom itself.
By such trainings, the kids would feel confident and they would eventually adapt to the changing situations in a positive manner.