[user104658]

Depends on the age of the child. Young children, yes, it's probably a parenting issue. Past the age of about 8 or 9 then not necessarily. It could still be that, but by that age, kids have a lot more freedom and frankly a parent who is watching their child like a hawk and controlling their every move / everything they eat is a far "worse" sort of parent, and is going to raise a far "worse" / maladjusted adult. There's only so much control that a parent has or SHOULD have over their children, and food issues are an absolute minefield. If you get it "wrong" when tackling them, you could end up triggering a life long eating disorder.

That said, a parent who can see that their child is overweight and isn't taking steps to find out why, and to help them to tackle it is definitely a "bad" parent, or at least, is making bad parenting choices in that specific area. Because a fat child is definitely not a happy child. There's something that needs to be addressed.