*disclaimer* Not yet watched vid. (Can't have sound right now, so waiting.)
I'm a mom of 2. The youngest inherited the "skinny genes" from my grandfather/mother/cousins. She's long and lean, and athletic (ballet dancer), like all of them.
My firstborn inherited the "diabetic genes": Always a little chunkier, less inclined to exercise.
These are 2 distinct types in my family tree, and I've seen them over and over.
I talk with my kids. When the firstborn started needing "husky" sizes, we discussed their genetic heritage, and the ugly realities of what living with diabetes meant... and that weight gain (particularly OUR type of weight-gain) would help cause that.
We talk about food all the time. Bread? Potatoes? Noodles? Corn & other starches? No nutritional value. Meat? Veggies? #1 nutritional priority, and a good way to stop being hungry.
I don't limit their food, but I encourage good choices. If we go out, YES, they can have pancakes if they really want them.... BUT. They have to order and eat enough fat and protein FIRST. Because otherwise, they'll be tired, grumpy, and sick-feeling in an hour, and the whole world will be treating them terribly. (ie: their blood sugar will have bottomed out.)
They don't drink milk or soda, juice only occasionally. My eldest likes iced (not sweet -- ew!) tea once in a while. My youngest will ONLY drink water unless she has a sore throat. (Then, pineapple juice is a special treat.)
I don't condemn "fat".... but I do point out things like genetic tendencies and body-shape warning signs of developing disease, and try to teach how to AVOID those long-term consequences. Belly-fat = diabetes risk... and the fact that I was diagnosed this fall brings that risk home.
Recently, the kids & I were traveling for the better part of a week... and I made sure they ate regularly, but wasn't eating myself. (Fasted from Sunday evening - Thursday morning.) I simply wasn't hungry. (I drank like a camel, mind you... but food didn't even sound good to me.)
My eldest teen couldn't conceive of this, so we discussed the biochemistry behind it, and they became more determined than ever to try to eat like me, simply over the concept of not being hungry.
(And when I did become hungry, on Thursday morning, I ate, and the kids saw that, too. I was hungry all day on Thursday, so ate meals "like a normal person". (Meaning 3 meals total, instead of my usual meal-and-maybe-a-snack)
I set an example, I talk about what I do and why, and I encourage my kids to consider their HEALTH (not their weight)