I was a 70s kid and meal sizes were mini compared to now. Plus not a lot of snacking going on.
So - a typical kid's meal would have been 2 fishfingers and a tablespoon of garden peas. And that would have lasted a child til next morning.
Cereal was the amount in those variety pack boxes. Some kids had one pack of crisps at school break. But it wasn't the huge family sized pack of today. It was the smallest size bags with 10 crisps if lucky. And you probably gave 5 of them away.
School dinners were hearty though. Maybe stew and dumpling plus a suet pud with custard.
Just water to drink. ⅓pint milk for morning.
Moving to teen diet. Well, i didn't hit teen til 1980.
I skipped brekkie altogether
I had nothing til lunch
Then one Hollands meat and potato pie with baked beans. And one bag of sweets (Revels usually small pack size)
Got home - usually raided the fridge for milk. Tea time would have been a breaded shape thing (rissole, remember Brunchies?! Fishcake, burger small)
Plus always garden peas. And that lasted me til next lunchtime.
I did a long paper round and was very active. I was 7 stone til early 20s at 5'4"
I didn't like fizzy juice/coke so never had that.
I thought i ate a lot of sweets. And i did have sweets every single day. But a lot was one individual sized pack of minstrels/revels/rolo etc.
I would not have had more than one per day. I did not like crisps much and rarely to never ate them.
I ate very little fruit either.