Regular Corn Flakes as a 'treat' is acceptable. Frosted Flakes or like sugar loaded corn flakes are not. Corn Flakes offer little in the way of nutrition for Adults, Kids or Parrots, they are more like fillers than a nutrition source.
Corn Flakes also contain fairly high amounts of Salt. So as a 'treat' from time to time its okay.
I let mine eat Grape Nut Flakes.
Does not have much sugar (at least I can't taste it)
Lots of vitamins (must do some good)
just a pinch in the morning. we aren't talking a spoonful here.
A crossover Quaker Scuti (F), A Sun conure named AC, A Cinnamon Green Cheek conure Kent, and 5 budgies, yellow (m), clark Jr. (m), Dot (f), Zebra(f), Machine (m).
I think the main point is your kids fed the bird cornflakes or tried to, this is fine, he can't eat to many in one sitting, and if it's not all sugary then it's an ok treat, and it's bonding. I wouldn't fill his bowl with it, but kids like to give treats and better cornflakes than gummy worms or something that would actually be bad for the bird.