People labor under the illusion that a two year old can’t pull a trigger. What a toddler does is put the gun on the floor, where the kid spends most of its time. Eventually, the gun ends up with the butt down, the muzzle up, both of the kid’s thumbs on the trigger, with the kid pushing down on the trigger as hard as it can. Any toddler weighs more than the trigger pull so it has the mechanical advantage to press the trigger all the way through, even on a double action revolver.
A head shot is almost the inevitable result. That’s why so many of these are fatalities and not just wounded casualties.