The parent commenter said "learning about computers". Most "professional developers" don't learn about computers, they learn enough react to get a paycheck, but don't have an insatiable curiosity about how the whole computer works (i.e. the "hacker spirit").

Professional developers are not what this thread is about. It's about curious kids, about hackers, and that group does peek at kernel source code (as well as everything else).

I’m fairly confident that the Venn diagram of (a) nine-year-olds that are playing with a computer and (b) people who claim that access to kernel source code is a prerequisite to “learning about computers” is two circles that are barely touching.