I agree on that letting a child be obese could be considered a form of abuse.
But talking about child's nutrition, there are many sides to this issue. If you look at it from the point of view of parents who have the possibility of giving their children a healthy and balanced diet but prefer to satisfy their whims and allow the child to eat what he/she wants and become obese, there is negligence. But what about the millions of parents who do not have financial resources, and give their children the food they can afford, which is never the healthiest. In that case, I do not think we can speak of negligence, although there is a problem of malnutrition.
The affordability of healthy food is another issue, but related for sure. However, I think that for the most part, to become obese actually is quite expensive, considering the amount of calories that are required, so it is unlikely a case of affordability of better options in many of the current cases at least.
However, the money argument isn't valid for much of the world where obesity is an issue and it isn't an issue around where I live, yet there are plenty of obese children.
When my wife was young, her parents kept getting called into nurses and doctors because they thought she wasn't being fed enough, yet that wasn't the case, she is just very small. However, none of the parents are getting reported for their children being overweight. Why the double standard?