Dr. Oz would be so ashamed of those of those of you wanting to put a child on a diet! Some kids (and many in recent years) struggle with weight - their bodies respond to food by storing it. Problem is if you look at the food they are eating - it is usually high in fat, carbs, sugars, and low in protein, fiber, and antioxidants. The children are borderline diabetic because of their diet - and they're just kids!
You need to take a serious look at what your family eats. Is it mosty processed food? Is it high in fat or sodium content? Does most of it contain cheese or dairy? Is it water based - meaning what percentage of your food is made from fresh veggies and fruits?
Does your child eat school lunch? If so - you need to start making his meals. A typical school lunch is this: chicken nuggets - made from the leftover bits of chickens and processed with so many unnecessary additives that it is in no way nutritious, tater tots or french fries - no need to explain the dangers here, canned fruit in heavy syrup, and 2% chocolate milk. There is no fiber, an excess of fat and sodium, high fructose corn syrup in the fruit and milk, excess carbohydrates, and more calories than a fully grown adult would consume in two meals if on a proper eating plan. Michelle Obama is right about reforming school lunches - they are not healthy right now.
As for home, if you find yourself opening store-bought frozen meals or preparing "meals in a box" more than 2 days a week you are doing your family a huge disservice. You need to make time to prepare fresh meals from scratch. This eliminates the "extra" ingredients that are in the store bought meas - preservatives, excess sodium, fats, and chemicals - all toxins to the body which produces a "store" body response leading to being overweight. Preparing those meals sounds daunting but it is not if you are organized, use a list, and prepare them ahead of time. Many meals you make can be stored in the freezer for quick prep when needed. There are a lot of internet writers you can glean suggestions from - just start looking.
Your food should be 70% fresh. High in protein and fiber. This is what keeps us feeling full, gives our bodies the energy we need to burn calories and build muscle in order to maintain a healthy body and not crave the junk.
Best of luck to your family and your son. It may be good to also take your son to a nutritionist and let her tell him the importance of eating right and how to do it. She may pull more clout than you - the mother hen.