This is five year old thinking. A five year old cannot comprehend gun safety.

[magical thyme]

80. logical thinking does not develop before a certain age, around 7 IIRC

And emotional maturation also plays into events. How many adults never got over their sibling rivalry issues? A first-born 3 year old who suddenly has to share attention with the new baby hasn't necessarily gotten over it by age 5. Combine that with lack of understanding of permanence, and what's to stop the 5 year old who's ticked off that the 2 year old usurper is getting attention from pointing their little rifle when mom isn't looking and going bang?

That rifle didn't point itself at the 2 year old's chest, and didn't fire itself either. Either the 5 year old was average, meaning he lacked logic, understanding of permanence, and forgot the rule about never pointing the gun at a person ever, and was just playing. Or the 5 year old was precocious, did understand what he was doing, and did it on purpose. Take your pick; can't have it both ways.

The brain develops in stages that are pretty well understood. Variation means within well-defined ranges. Outliers are rare and to assume your child is the outlier is just plain foolish.

There's a reason why we don't allow driving on public roads before age 16, and then require a training period and testing.