You'll need to do a full back, round chest and tummy adjustment and account for the negative ease. Weird cross of men's corpulent adjustment (chest) and women's (hip and back). Although you can do a FBA as long as you realize it's width and not breast weight. And yes, I know it is a kid.
You can also grade up where needed, and realize some pieces are going to grade different then others. IE: the belly may need to be graded from under then arm seam to the waist, then the full belly adjustment from the waist to panty. While technically the same, on a pattern they don't always come across the same. Same with the back: the shoulders and upper back may need it, and then not the waist, but then a flat seat adjustment. And it can wind up looking like you have 3 different patterns in one when finished.
The easiest is to take the pattern and make the adjustments to the pattern, make a muslin and pin it on the kid, then take that and transfer it to the pattern.
The pattern is not going to be elegant looking in any fashion and will not really result in hanger appeal when finished, but will look good when on the body. The biggest trick is to keep the balance and work on the individual areas and not all of them at once and not to work from the side seams.
Even though it's not a woven, those tricks still apply, just make the ease negative.