Summary:
My best
guess is this: If you have loaded any of the mods below I have looked at/guessed at, then its likely your son has found and read the book "Art of Mining Vol 1" and you have not. Once you find and read this book, you will likely be able to find brass when mining the same boulders.
If you do not have this book already read for your character, and your son has this would make some sense. If you want to prove this is what is happening with whatever mods you have loaded, and wanted to cheat a little vs finding/buying the book, you can go into the games cheat menu and give yourself the book and read it. I don't believe you can "take it back" though so once its read its read forever for your character.
Details:
I can't load the mod launcher because I'm not using windows... and all the mods I'm finding indicate "18.4" game compatibility, but some other things indicate a19 compatibility, so maybe the mod author(s)/maintainers are not updating the ModInfo.xml data for a19?
It *looks* like the mod name is "Harvestable Brass". Here's a link to it:
https://7daystodiemods.com/harvestable-brass/ which says its for "alpha 18" of the game.
BUT! this leads to this forum here:
Which then leads to here;
https://gitlab.com/army.bratt44/mods which then says "Unforgiven and tonys Brass From bolders"...which may be a different mod...but says the game version is "18.4" even though the gitlab "commit notes" indicate alpha 19 compatibility
ANYWAY: It you look at the mod, its 1 blocks.xml file, which has this in it:
<blocks>
<append xpath="/blocks/block [@name='terrOreIron']">
<drop event="Harvest" name="resourceScrapBrass" prob="1.07" count="50" tag="artOfMiningLuckyStrikeHarvest" />
</append>
</blocks>
which seems to indicate that the "brass harvestability" from iron boulders is linked to the "Art of Mining" perk trees, "Lucky StrikeHarvest" which appears to be given to you when reading the book "Art of Mining Vol 1"
HOWEVER! I found another mod called "Brass from Biomes" that has the same author(s) but is different, internally. It also says "18.4" compatible but has more "in the mod" so its likely a newer mod? anyway, it has similar logic in it except the "brass from ore" icon looks like a goldish/brassy ore blob (the kind you can only smelt in the forge to then get the brass as a crafting item), whereas the other mod uses the standard 'brass" in the vanilla game...
