I have the very lean, twiggy, ravenous type of children with a major genetic advantage, so I'm not going to claim all the credit on providing them with a virtuous lifestyle.
Our diet could be better. An advantage of not living near relatives is that we don't get the weekly rourine"treat" from grandparents. We do get a lot of sweets home from school so I feel no need to keep a routine stock at home. I have no gripe with school desserts as portions are small and they're not the 700+ calorie slab you'd get at the pub. I managed a school life and teaching career with a school dinner and dessert for 25+ years with no issue. The only desserts we have regularly at home are when certain fruits are in season in our garden.
I've fallen into the routine of activities most nights across cooking time. Unfortunately DS1 is very sensory so a lot of one pot meals that are ideal to prepare in the day time are out. I do have the advantage of living near school and community facilities so we do walk daily to school in EVERY weather (in grim weather the cars come up to next door but one, but one's house so I have no motivation to drive) and to several activities. Swimming night we are out for 3 hours, for a 30 minute swimming lesson each. For the value of skill gained it's an investment long term, but it's a poor amount of activity time for that window. That's time not spent out in the garden being active.
I ask my DCs "Is your tummy happy? Is your tummy going to be happy until... (insert next meal) There is no pressure to finish the plate in a society of abundant food. I didn't fall down the pit of regular snacks as toddlers to need breaking. They are ravenous when they get in from school and they're better off having a "light tea" rather than grazing on snacks without being sated. I generally avoid certain aisles of the supermarket. We drink full sugar squashes rather than sweetners, but mainly water.
I'd like them to eat more vegetables. Unfortunately there are a lot of clashing tastes in the household and the DCs don't eat slimy lumps of veg in sauces, and DH is no fan of faffy "Sunday dinner veg" which uses up a lot of pots to keep them separate. It was a lot easier to feed them as toddlers even with multiple allergies to cater around!
Children's "healthy" products are often not that healthy and encourage a grazing culture.
In town, McDonalds is half the price of trying to find something more nutritious... and actually it probably isn't vastly better anyway! There's deserts parlours everywhere, portions are huge, bucket-like mugs of hot chocolate covered in cream and marshmallows. Massive portions are normal not a rarity which distorts perceptions.
It is a tough battle against society at times. Watching my DS's class growing up, the ones that were a bit chubby and toddler-like in yR are now definitely fat by junior school. In a few years there probably will be outcries when the school measuring is carried out. The gap between 5 and 11 is too great and there should be an extra stage at 8 before puberty kicks in for the majority.