If starving a child is child abuse then so is feeding the child to total excess. There should be leeway if the child has a medical condition, but most very overweight kids are caused by very poor diets. Children are not old enough to decide their own eating patterns so it is up to the adults in their lives to help them.
Obesity is a complex issue. It is an epidemic in America, a society that idolizes thinness. You would think that if it were that easy to be thin, people would just do it. But the truth is that there isn't a single cause. Genetics can leave a person dispositioned to obesity, and so can poverty because unhealthy, high calorie foods are cheaper than healthy, nutrient packed foods. Also the agriculture industry keeps putting additives in our foods, like growth hormones, which can have an impact on human health.
Based on these three factors, how could you blame the parents and make an acceptable argument for why the parent is abusing their child because their child happens to be obese?
Yes, it's the parents job to make sure their kids have a healthy diet, limit their snack, try to get them to drink more water and get them to more active. But if their kid is obese, that doesn't mean the parent should go to jail for child abuse. Child abuse usually involves bodily harm to a child and can leave long lasting mental scares. You can help a child loose weight by getting them to eat better and have them become more active. With child abuse, you have to send their to therapy and it can take years for people to get over those issues