I grew up on porridge and I still eat it every morning with my coffee and toast
I think it was the difference between me being a good student in elementary and high school compared to my classmates who all barely passed or just dropped out. This and a steady diet of fish at least twice a week when I was growing up.
We never had a lot of food because we are Indigenous Canadian, grocery food was way too expensive so mom and dad relied on wild food and wild fish to supplement our diet ... I estimate about half my diet before I was 15 was wild food. The only cheap thing mom could buy for breakfast was oatmeal and its something I've eaten every day of my life. Milk was a luxury so most of the time, it was just watered down canned milk every morning.
I don't have kids of my own but I have lots of nieces and nephews and I see what they are living on now. Almost 100% store bought food and sugar laced boxed cereal every morning. Almost all of them are either chubby or just plain overweight. I look at pictures of me and my siblings when we were ten, and we looked like skinny scrawny kids .... my nieces and nephews are now all overweight at the same age.
It's not just the quantity of food that is important ... it's the quality of the food we eat or feed to a child.