My sims almost never burn food because only a Natural Cook is ever allowed to prepare meals. It's one of my favorite traits, and when no one in my household has it, the sims subsist on quick meals, fish or veggies toasted over the fire pit, or baked goods from the child's toy oven. (Yes, even for breakfast. If I'm going to make them too lazy to learn how to cook, I might as go all the way.) That's the only time anything gets burned—since children can't have the trait, they mess up quite often. This seems realistic.
On the other hand, I try to have sims in good moods when they're skilling up, since their progress is so much faster, so neither children nor adults are likely to cook when their hunger meters are in the red. The burned cookies are probably coming out of the oven after everyone's fed already, so it's not a problem for the kid to make another batch.