Final answer:
Alejandro's recognition that his mother has more Cheerios than him, and his subsequent emotional reaction, relate to the concept of theory of mind (TOM), which refers to the understanding that others have different thoughts and perspectives.
Step-by-step explanation:
The scenario you described with Alejandro crying because his mother has more Cheerios than him is related to a core knowledge system. Specifically, this incident is reflecting the concept known as theory of mind (TOM), which is a cognitive ability that develops in children between the ages of 3 and 5. Theory of mind allows children to understand that other people have thoughts, feelings, and beliefs that are different from their own.
In Alejandro's case, he is recognizing a difference in quantity between his bowl and his mother's, and is expressing his understanding that they each have different amounts. His emotional reaction suggests that he desires equality or perhaps more for himself, which at this stage of development, is characteristic of a growing awareness of fairness and perspective taking, key components of theory of mind.