Why do you need a pediatric surgeon, per se? Bariatric specialists can do surgery on people of all ages. Do you have a bariatric center near you, or is there a hospital with a bariatric clinic in it? Personally, I wouldn't seek surgery on a person under the age of 21, which is where scientists say we pretty much stop growing and developing. This could backfire. But there may be a less invasive type of procedure you could perform on a child.
And really, the first step and a step we all take either before or after, is teaching the child about nutrition. And controlling sugar is really hard with kids, but weaning your child off tiny amounts at a time often works best. I remember when I decided to reduce sugar in my diet. It was a huge problem, and I went back and forth. But ultimately, sugar started to be pretty gross and using less was easy.
Don't sub artificial sweeteners. Instead, introduce fruits and naturallu sweet foods in small amounts, and do add a little sugar as needed, but really just a tiny bit. Tastebuds adapt, and then cravings reduce. Best of luck to you.