Assuming your DH is a doctor with some knowledge of this stuff, what does he think?
There is no doubt in my mind that many parents are in denial about their children's weight. Having said that, there's a limit to what you can do when your child is this young and you have to be realistic.
DS was overweight. We knew it. Not crazily so, but clearly overweight. I discussed with the doctor. Her point was that at that age, restricting food is not advised. Exercise, healthy, varied diet is more important.
A few years later, we did have to take a more proactive approach because by then he was more overweight. He was also old enough to understand this. Part of fixing the problem was me and DH, as his parents, taking a long hard look at our OWN behaviour and what WE were doing.
We had to acknowledge that that he WAS having more treats and food that was high in sugar and/or fat than was good for him.
But we also had to acknowledge that as a tall child who genuinely has bigger bones than others, he needed more/different exercise than other children. I came to realise that he wasn't always incentivised to keep moving when he was outside and that he was more of a burst of activity type of kid. But that wasn't going to help him with the weight.
We also looked at his "healthy" food. And had to realise that traditional kids food wasn't good for him. If DD eats something like shepherds pie its a good dish for her - protein, carbs, veg (on side and hidden). But for DS, who loves food, he will eat a big plate of whatever is served to him. if that's shepherds pie, it might be very nutritious but a b ig plate is too many calories. As a good eater, we could switch to serving him the kind of meals many younger children wouldn't eat - a piece of salmon with rice and piles of steamed veg or baked chicken with salad and new potatoes etc - allowing him to have a large portion but without the same number of calories.
None of these things would have happened if we'd continued to be defensive : "but he eats normal healthy food" or "but he does lots of activities and is out and about all the time."