But most importantly, in order to buy a gun you need to get a license. This means medical check, passing a theory test, passing a psychological test and passing a practical test at the shooting range. It's not trivial at all.
The culture is completely different to US. Everyone is keeping their weapons in a safe. No bedside tables, car glove boxes or other nonsense. I've never heard of a child taking their parents' gun.
Qua guns, teenagers in other countries don't have easy access to concealable firearms. Dad doesn't have one, and you can't waltz into a store around the block to get one.
The Uvalde shooter purchased his weapon a few days prior. Most school shooters do. Anything making that harder helps.