Tell him to search Operation Paul Bunyan as well as pictures of the height/weight disparity of north korean soldiers vs american soldiers.

It's best to take a humorous trash talking approach with these kinds of subjects and downplay any north korea bullshit as opposed to lame downplay of like 'it's okay son, we'll be fine.' It's not patronizing, but it just doesnt with a 13 year old who's coming into the 'my parents are dorks' stage of his life.

Say something like this: 'I get it: you haven't been around the block to see this before, but they always do this. We can and will rock the SHIT out of those malnourished fools if they so much as scratch their ass the wrong way. Sheeeit, you know they really done goofed up when even China is on our side this time. We literally have them surrounded on all sides with the most advanced militaries on planet earth ready do fuck up a bunch of 4'9" skeletons with 70s-era equipment. It'd be like if an anorexic danny devito tried to start something with Maywhether, Ali, Tyson and Forman all at the same time. all this hype you're reading about is just the result of a bunch of whiny, buddy-holly-glasses-wearin' writers trying to squeeze as many clicks as possible out of north Korea actin' a mothafuckin fool again with overly dramatic headlines. we'll be fine, kiddo.'

and now they're looking up all the information with a new sense of 'oh damn, are we really that strong? are they really that weak?' The best way kids can learn is if they seek out information for themselves, as it feels empowering to begin to form their own opinions. Humorously guiding him in the right research direction is both beneficial for future information acquisition as well as an anxiety-alleviating jab at a statistically marginal army.