This happens because Jamal and Jovani are in different stage of their cognitive development, which indicates that reasoning ability is very different from both children.
In this case, Jamal is in the stage of concrete operations, this stage covers from 7 to 12 years, and the development of the logic is observed to solve the problems, develop the capacity to understand about the preservation of the matter and they leave egocentrism.
On the contrary, Yovani is in the preoperational stage, which covers from 2 to 7 years, at this stage the child cannot logically still reason, or perform mental operations, so Yovani's reasoning is limited to analyzing things according to what he observes.