The children's grades are simply a grade that goes according to the knowledge acquired during the school year. This, of course, can be linked to many circumstances that can make the grades not good or that they can be improved.
Many children feel anxious when they are given the report card, thinking that their grades are not enough and that they are unable to do things differently (if the result is negative).
Children need to feel that they are capable of improvement, since only in this way will they be able to have enough motivation to be able to work during the holidays and reinforce things such as reading, writing or some concept that has stuck during the course. If required, point your children to summer classes, but in no case should it be a punishment, if not, they must understand that it is a help to improve themselves for the following course.
Punishing children all summer for poor grades is not a good idea, because even if you think it will improve their performance, if it does it will be out of fear. When there is a change in behavior out of fear, the change is not actually internalized so in the long run, you will probably have an aversion to studies, falling in the probability of suffering school failure.
In this sense, children must have clear consequences according to the marks they have obtained, previously agreed upon and agreed with them. For example, if you have had a poor performance due to lack of organization in the study, you will have to go to a psychopedagogue to teach you how to study. If it has been due to behavior, you should work on self-control, etc. It is necessary to find the root of the problem and then find the most correct solution according to each case.