It doesn't exist any more. BMI cutoffs for overweight and obese are based on the percentiles pre-obesity epidemic. They're based on a previous generation of kids.
My state has 24% of third graders measuring in an obese BMI. 24% of kids fit in the curve where 5% of kids used to. It's the new normal.
At some point as a society we have to become "obsessed" with this [what I would term "have a normal reaction to this"] for the sake of the kids. It's very messed up. Whether it's the BPA or the current paranoia about kids walking and biking to school and activities and playing outside unsupervised, the rediculous stuff that passes for school lunches, or whatever, it's not something to poo poo.
This has nothing to do with the OPs kid, who is not obese. But look, the idea that being overfat is OK because "someone has to be" isn't good for our kids. There are times that it's the best a family can do, but there are times when perhaps a family can make some changes, and the rest of us can start providing fruit and cut veggies for our snack turn at Scout meetings, instead of chips and cookies.
This is a video out in our state because of the high levels of childhood obesity here that parents are facilitating. http://strong4life.com/stopthecycle/