First you have to figure out which side of the argument you are on. Are you for disciplining children or against it? Once you do that you can create your thesis. One example if you are for disciplining children is "I believe children should be disciplined because it helps them grow into successful adults," or if you are against it, you could say, "I do not think children should be disciplined because it can cause mental issues later in life." Remember these are just two examples highlighting two different subjects.