I would stop most of that tbh. I think it's just sets up bad habits in general and unhealthy for teeth as well as them getting less vitamins than if they ate something healthy at those points
I would scrap the galaxy drink altogether, they really are terrible for teeth and just warm regular milk instead
Then just give a piece of cake or choc each day max.
I also have slim children. Both around 50% for weight but off the scale for height / around 99% sometimes. So it would be easy to just let them eat whatever as they obv can eat more as taller than average and excercise loads. However I know that at some point in the future they will stop growing in height and that's when they may gain weight easily if eat lots of he wrong foods
We make ice lollies in summer with just milk and fresh fruit blended. They rarely have desert as if full from dinner won't eat more, but if so it's just greek yogurt with berries ad down honey maybe. They rarely snack either but snacks are nuts, cheese, boiled eggs, fruit, raw veg,
Cake is generally just at birthdays they go to , or occasionally we bake some. Chocolate is only at Xmas/ Easter/ Halloween etc, and most of that gets eaten buy adults also then binned if too much