I have no real experience with the kind of problems you are having as I have never taught children at that age.

The reasons for the children ignoring your instructions can be manifold - they may perhaps not understand or appreciate you, you may lack authority among them, they perhaps like to try out how far they can go with you as a foreign teacher, etc. If it is anything in this way, then it shows that there is a basic problem for you of becoming a real part of the local community (which, of course, is not your fault in the first instance).

Foreign teachers dealing with older students can sometimes face the same problem - I have once had this kind of problem as a university professor with first year students at a university in Korea - my requests for a bit of silence in the class were constantly ignored. There was real noise so that I could not do my classes in the way as they should be done. Yelling, complaining etc. in these cases won't help much. Instead, I decided to meet with some of these students privately after class, inviting them for a meal in a restaurant. At the meal, I told them about my feelings as a foreign teacher and added that I do not feel so well and that I would leave at the end of the semester. The students were quite astonished to hear this and asked for the reasons which I then explained to them.....And, you would not believe it - the next day in class, all of them were quite different - no noise and other disturbing things anymore...it is the first time that they had shown some kind of basic respect for a foreign teacher ....as I felt. From then on, I have never had these kind of problems anymore.

In your case, it would probably more difficult to find a solution this way - your students are much younger and not those 18-19 year old young adults that I was dealing with.

In your case, I would urgently advise that you secure yourself the assistance of your native teacher colleagues in the matter. Talk to them about the problem and ask for advice and help. Maintain a good relationship with them. Mostly then, these kind of problems will disappear after some time. And have a bit of patience, please!

Good luck!