I'm no longer overweight, but I was throughout childhood. It was a misery, I didn't enjoy my life much...
However, it was my fault. I started putting on the weight, when I would sneak food - I wasn't obese, just overweight. When I reached Secondary School, I was obese - I would eat behind everyone's back. That isn't my parents' fault. They were not abusing me, I was abusing myself.
Like I said before, it depends on the age/how they got obese. It isn't always the parents' fault, and it also isn't abuse - it's poor parenting, if they're small children, but even then, no one knows the circumstances.
I'm not making an excuse - I'm really not. I will do my upmost to make sure my children never become overweight/obese. My childhood was no fun, I never did any of the activities I wanted to - I was too self-conscious. However, the spectrum is too large, and would need to be looked at on an individual basis to really say if it's abuse or not.