No. I think some kids just get really really big. After watching the show "My 600 LB Life" I kind of think it's a genetic disorder. My little brother was fat when he was a little kid. Now he's lean and he works out all of the time. You never would have guessed that he was really fat and overweight when he was 10. He started losing the weight when he was 12. He got really skinny.
lack of education (ignorance), limited access to healthy, affordable foods are often times the case. sometimes its a vicious circle where the parent who is obese themselves, feeds their kids like they were fed (and never educated on what's healthy) and the kid ends up obese like them. sometimes it's completely negligent and the parent ignorantly claims that their kid will be fine if they knowingly feed them healthy foods. perhaps both ignorance, shame, and an inability to accept their parenting skills are creating unhealthy habits are to blame. so yeah in a way id say its bad parenting, but sometimes its legitimately a socioeconomic factor and lack of education