In his new book “Fear” on President Trump and his administration, journalist Bob Woodward wrote the following account, according to this Washington Post article:

At a National Security Council meeting on Jan. 19, Trump disregarded the significance of the massive U.S. military presence on the Korean Peninsula, including a special intelligence operation that allows the United States to detect a North Korean missile launch in seven seconds vs. 15 minutes from Alaska, according to Woodward. Trump questioned why the government was spending resources in the region at all.
“We’re doing this in order to prevent World War III,” Defense Secretary Jim Mattis told him.
After Trump left the meeting, Woodward recounts, “Mattis was particularly exasperated and alarmed, telling close associates that the president acted like — and had the understanding of — ‘a fifth- or sixth-grader.’ ”

For the record, Mattis denied saying it after The Post's report came out.

But many fifth- and sixth-graders in the United States might well understand the significance of the massive U.S. military presence on the Korean Peninsula (surely they do in South and North Korea).

U.S. students in fifth and sixth grades are at the end of elementary school or in their first year of middle school. Fifth-graders are usually 10 or 11, and sixth-graders 11 or 12, and they learn some pretty complex ideas, even in elementary school.

To be sure, many students with Korean roots and connections to other parts of Asia probably learn about the history of the U.S. presence on the peninsula at a young age from their families. And there are more than 60,000 U.S. soldiers stationed in South Korea and nearby Japan, many who have children who learn why a loved one is there.

For children who don't, social-studies standards in various states show that students in fifth and sixth grades are learning about major events from the 20th century and the emergence of the United States as a world power. That could easily include lessons on U.S. involvement on the Korean Peninsula.

Let's take, for example, Utah's social-studies standards, created by the Utah State Board of Education. This is part of the standards framework for fifth-graders:

V Students will address the causes, consequences and implications of the emergence of the United States as a world power.
1 Describe the role of the United States during World War I, The Great Depression, and World War II.
   a) Review the impact of World War I on the United States.
   b) Summarize the consequences of the Great Depression on the United States (e.g., mass migration, the New Deal).
   c) Analyze how the United States’ involvement in World War II led to its emergence as a superpower.
2 Assess the impact of social and political movements in recent United States history.
3 Evaluate the role of the United States as a world power.

And in sixth grade, the Utah social-studies standards say this:

Standard 4 
Students will understand current global issues and their rights and responsibilities in the interconnected world. 
Objective 1 
Analyze how major world events of the 20th century affect the world today. 
Objective 2 
Explore current global issues facing the modern world and identify potential solutions. 
Objective 3 
Determine human rights and responsibilities in the world. 
Social studies language students should know and use: environment, pollution, political turmoil, poverty, famine, child labor, conservation

Other states have similar standards in which fifth- and sixth-grade students have a chance to learn about the world and the 20th-century history of the United States, which could include a lesson on the Korean War and its aftermath.

In the earlier grades, many students are exposed to different cultures and world geography, which could include a discussion about the Korean Peninsula, especially in classes with students with roots from that region. The Massachusetts standards for second grade, for example, say the following:

Topic 2. Geography and its effects on people
Supporting Question: How do people adapt to or change their environment?
Topic 3. History: migrations and cultures
Supporting Question: What are the different reasons people choose to settle in a community?
8. Investigate reasons why people migrate (move) to different places around the world, recognizing that some migration is voluntary, some Forced (e.g., refugees, people driven from their homelands, enslaved people).
9. Give examples of why the United States is called “a nation of immigrants”.

Meanwhile, some sixth-graders read books with difficult topics, such as the World War II account “Anne Frank: The Diary of a Young Girl."