Some people I know can eat practically unlimited amounts, do very little activity and not gain a millimeter of fat. Other people with very slow metabolisms (like me) can't eat any junk at all and need to sweat every day if they intend to be fit.
If your kid is staying at a healthy weight, let them eat whatever they want. But if your kid starts ballooning like I did, it's wise to start watching out for them. Nomatter what BS anyone says, it greatly diminishes your social life and general well being. Obesity during puberty also causes hormone imbalances that could result in development issues in nearly every part of the body, especially in boys. After puberty, there is not much that can be done to correct it.
I really really wish my parents taught me better eating and exercise habits when I was younger. I'll naturally never be as developed and fit as I could have been.
“I was never denied any foods as a kid and became a junk food addict for a long time.”
There is a basic, psychological principle that is even described in the bible. If a person is told they can’t have something, they want it all the more. I don’t know what your issues were. I spent years wondering how so many, very wealthy, young women were so skinny. I had the revelation that it was because they could have/eat whatever they want, just as the scientific studies showed about children essentially getting bored with junk food and choosing nutritious food instead. It’s about options. I cook healthy meals, the aroma’s are in the house, and that wins out over the junk. I don’t make an issue out of food. I cook. If someone wants to eat it that’s fine. If more family is around and we make it a social event, that’s ok, too. Food isn’t the center of our lives. Making such a huge issue over food and nutrition is one of the things that creates problems in the first place.