As a therapeutic parent, I've seen many kids with brain damage from fetal alcohol spectrum disorder who come from a long line of addicts and because of the FASD impulse control issues and sensory and emotional regulation issues and family history have a very addictive nature. One tried to drink the little tub of unused pancake syrup at breakfast despite me loading his plate his plate with health foods and talking about their importance and diabetes and heart disease and how uncomfortable obesity would be for years.  I had another who stole some crusty old lollipops from Halloween 8 months earlier I hadn't tossed from the back of the pantry when it was left open ( you have to lock it because food insecure kids will do crazy stuff like hide perishables under their bed so they don't or that one time I got a phone call and a preschooler scarfed 3/4 of a family sized box of cheerios in 4 minutes because he was so afraid of not eating again). I do my best to undo those bad habits but you can't always undo such significant early trauma and FASD is permanent brain damage, so while they may fall within the normal IQ range, they don't make decisions the same way. Is it really my fault if they end up fat?  Yes I know I'm an extreme example but what is the one thing you really can't control about a person's body without crossing into abusive behavior, or even that easily if you would be willing to cross that line- what goes in or out. So a lot of kids use that against their parents and not always just these sort of extreme ones.