I will probably be in trouble for saying this, but imo the issues in the UK are:
- portion sizes being overly large and then children being trained to finish everything on their plates thus over-riding the body's full signals.
- far, far too many carbs. Before we had DD I never had bread or biscuits in the house as they're horribly addictive, and I try to not always have potatoes, rice or pasta at every meal. Grated cauliflower is a really nice rice substitute (and I generally loathe cauliflower).
- too much convenience food which is high in sugar - especially hidden sugar.
- snacking between meals. It's very habit forming and just makes you hungrier.
It is the case that it's hard to cook healthy food quickly on a budget. A large pack of sausages (often containing bread so carb heavy) from Iceland, with a load of oven chips (more carbs) and some bread & butter on the side (more carbs) is probably cheaper than a bag of apples.
We've lost the knowledge of how to use cheaper cuts of meat (and no local butcher to make suggestions or explain), or make dishes that will last several meals - and with so many working parents it's hard to find the time to do this.
Whenever I'm in the supermarket and see a very obese family, I can predict that their trolley will be stuffed with carb-heavy foods - crisps, biscuits, large loaves of white bread and lots of convenience foods. I'm rarely wrong.
I know it's not always simple especially with children:
I struggle with a child with a medical condition which means she is never hungry (missing the hormone which helps control appetite) - and is also immensely picky. The only vegetables I have ever seen her eat are those disguised in sauces. We tried BLW, but until she was 2.5 years she was 80% breast-fed. The hospital were involved from when she was a year old and said to keep going on the bf as she was at least getting some calories that way.
As a result we have DD on a high fat, high calorie diet - she's still skinny as a rake and you can count her ribs quite easily. She can have as many snacks as she likes - but rarely wants any. I'm the mother trying to cram chocolate donuts into their child on the way to school!