Haha you're brother reminds me of me when I was a kid. I grew up during the time of the "family pc", where the household shared one PC that was usually in the living room. When I was 6 or 7 I completely ruined windows by deleting files I shouldn't have, or moving system files from C to D to free up space on the primary drive. Once I got older and figured out where the screwdrivers were, I started fingering every part of the pc and eventually ruined 2 HDD's and a mobo. Dad was livid cause PC's were an expensive luxury still, considering it was 2000-2001. Eventually I got my own PC by 2006, and I ruined that too, but only software issues that were resolved with a clean install of Windows. But my curiosity really taught me a lot about PC's, and I'm really in command of tech and being able to learn and adapt to new pieces of tech.

Point is, your brother's gonna be a whole lot more apt at working PC's when he gets older if he continues his minor curious fuck ups. Like don't give him a free hand to fuck shit up, but also don't discourage his behaviour. My dad says the same: I caused a lot of damage growing up but now the entire house and it's tech functionings are something only I can help them out with with ease.

TLDR: Let the little brats be curious, but within confined limits.