I'm obese myself but I still see my child's weight problems as being a real issue, there is no reason I want to shame my child, because I've accepted as an adult that being overweight is something I'll live with given the choices I've made and nobody should make that decision for me. If I choose to remain overweight, that's my choice alone and no shaming will change it.
But a child doesn't have to live with those choices yet, they're still a child, and as an adult who knows better I have a duty to give my child the absolute best start possible.
That's not just making choices for them and enforcing healthy diet and activity levels. That's teaching them about how to make those choices themselves, educating them, teaching them to be confident in their own skin, whilst also helping them to understand that some things aren't great for them, and being overweight is one of those things. If they chooses in future (as an adult) that being overweight isn't something they'll worry too much about, then I won't be shaming them either.
I don't want to teach my child to define themselves by their weight, I want to teach them that healthy choices mean life is more comfortable and longer, particularly given the disabilities I have and may pass on. So I am not about "fat shaming", but I am also not about allowing neglect to teach my child that they're not worth that effort of a healthy start to life.
Weight is just one part of neglect I am fighting, there are other things that show lack of healthy diet and opportunity to be active are just insidious to the general neglect going on in my child's life. So yes, allowing a child to be overweight can be neglectful, but I believe the neglect is where the parent could educate themselves to make better choices for their child and doesn't, or is told by health professionals that they need to make changes and don't, not in the child becoming overweight in the first place because that's easily done and can sneak up on you.