I agree - most cereals are rubbish. Porridge is probably the simplest (and cheapest). I would have been very unhappy about my toddler being fed the sort of low-quality foods the OP mentions.
However, I can't help noticing how much carboydrate-heavy food most people feed their toddlers. If my toddler hadn't eaten since the evening before, I'd assume he needed protein to start the day. What's wrong with an egg (boiled, scrambled, whatever) with a small piece of bread and butter - plus milk, obviously, for breakfast? People seem to regard lots of fruit as a healthy option, too, but it's full of sugar and isn't exactly sustaining. It's fine for snacks.
At that age, mine had an egg or cheese for breakfast, with a very small amount of bread and butter and milk to drink. If they were extra hungry they'd have a small bowl of porridge with honey as well.
My four babies were big (between 9lbs 2 and 11lbs 3), breast-fed exclusively until 6 months, and were on the plump side until 2 years old, when they quickly lost their "baby fat", so they weren't poorly wee things with no appetite.
I fed them a high-protein/low carbohydrate diet, though we didn't call it that - it just meant meals were based on meat/fish/cheese and eggs with vegetables and small quantities of things like bread/potatoes/rice. They did have puddings, but they were physically very active. When I eat out these days, I'm amazed by the portions served to toddlers - I suspect we're training them to eat more bulk than they need.