When your kid is changing his eating habits in order to lose weight, you need to lower your expectation! As adults, we know that at the beginning of a diet there is usually a rapid decrease in weight as a function of making dietary changes. In children and teenagers, it will not necessarily be so.
Because the child body is growing at the same time, sometimes you will not see the change on the scale, even if the child is doing everything right. Therefore, you have to understand and communicate to the child that “we are here together for a process”. It could be fast but it could also be last for a long time, but as long as you know you are doing it in a healthy way, you are on the right track.
You, as a parent, need to have patience and not be disappointed when there are no immediate results. Parents who expect the change to be fast, sometime reflect it to their child and could damage their chances to success. Show your support to you child diet and lower your expectations.