Editorial: Contrary to popular belief, teaching preschoolers is not especially difficult, for they develop strict systems (e.g., for sorting toys by shape), which help them to learn, and they are always intensely curious about something new in their world.
Given
Preschoolers develop strict systems (e.g., for sorting toys by shape), which help them to learn.
Preschoolers are always intensely curious about something new in their world.
Conclusion
Contrary to popular belief, teaching preschoolers is not especially difficult.
Evaluate
The argument needs to consider both the things that make it easier to teach preschoolers and the things that make it more difficult to teach preschoolers. Only after all the factors are taken into consideration can it be judged whether it is indeed easy to teach preschoolers. Any point that would make it less easy to teach preschoolers would weaken this argument.