I buy all sorts. It's cereal. Not crack cocaine.
Sometimes ds choses weetabix or shreddies. Sometimes cocopops. Sometimes toast or fruit. As long as he eats something before school I don't give a shiney shite.
Dd hardly eats anything in a morning, so if she fancies a bowl of cocopops I am winning at parenting.
Dd is 14, a size 8, tall and skinny. Ds is almost 5, in age 5 to 6 with the waist pulled in a bit. He has chunked up a bit over summer but walking to big school everyday and running around will soon slim him down again.
I cook most other things from scratch. We have 2 outdoor hobbies/sports. We walk the dog at weekends, we are outside a lot. Dd eats a fuckton of veg and fruit as a vegetarian. Ds eats fruit but is a veg refuser unless I hide it, which I do.
If they were having cocopops for breakfast, mcdonalds for lunch and a kebab for tea I would worry. But it's about getting a balance.
Some of dds friends weren't allowed sweet stuff as small dcs. No sweets, no chocolate, no sugary cereals etc. Now they have access to their own money they are bingeing on them. Dd had a bit of chocolate if she fancies it. The rest of her money she saves for clothes or makeup.