Things have already been covered but I'll share how we did things.
My kids are adults now but I had slim children.
They had 3 meals daily.
Breakfast. They only had cereal as a treat. Things like coco pops, frosties etc they had on holiday. It wasn't an obesity thing I just heard a comment about cereal being shit in a box and it put me off! ( im fickle, I know!)
Day to day breakfast was Greek yogurt ( not flavoured pots) with puree apple or chopped banana or similar or poached egg on toast.
Ds rebelled at around 14 saying he didnt want breakfast so we compromised with a home made smoothy.
Lunch was something like home made pasta bake
Tea. We all sat at a table and had a main meal such as stew, beef casserole, stir fry etc A couple of times a week we would have a desert.
I didnt and still dont buy crisps, sweets, cakes and snacks in as a part of a shop. Of course we ate things like that but it was bought in as a treat individually. They weren't banned and if the kids had some pocket money and wanted some sweets that was absolutely fine.
We did have takeout pizza, maybe once every two months.
The vast majority , if not all of meals were cooked from scratch including all sauces, pastas and breads. This was 30 years ago. Both me and dh worked full time so mostly it was easy healthy quick meals and we use a bread maker. Dh used to batch cook on Sundays if I was working. Funny enough both sons batch cook their lunch for the week.
This lifestyle has carried on to both my sons in their own homes. They cook mostly from scratc, have very few upfs. It's funny seeing how your children become a copy of you!
Neither of them have a sweet tooth.
Dont get me wrong, I love ice cream, coffee cake, a packet of malteasers or a packet of biscuits with a coffee but its not an everyday occurrence.
The other Important thing was for the children to be active. I didnt go out of my way to do this but me and dh were already active people. We took the children cycling and then later mtb, walking, progressing to hiking, progressing to multi day hut walks, bouldering progressing to climbing and so on.
I'm not suggesting this should be everyone's normal but I do believe children need to be active and family activities such as walking, which is made into a fun activity benefit the whole family.
Dont do what my mum did which was to weigh me every Sunday and have my dad say ' Jesus's Christ, have you seen the size of that!! ( I.e. me) She still goes on about my weight, whether its good or bad at any particular time and im 61 for goodness sake! 😆
Im not saying i got everything right but things seemed to work out.
Its just a shame I let things slip when I got depression and the menopause kicked in at the same time!!!!