Why do adults leave loaded guns within children's reach?

[Updated from 4/26/16, 7:55 p.m.] Concealed gun carry mad recklessness:

Idaho.  

HAYDEN, Idaho — A mom shopping at a Walmart store died Tuesday after her toddler, who was left in a shopping cart, reached into her purse andaccidentally discharged her handgun, authorities said. 

Veronica J. Rutledge, 29, of Blackfoot, Idaho, had gone to the store in this Coeur d'Alene, Idaho, suburb with four children in tow at mid-morning.
Her 2-year-old son, who was sitting in the shopping cart, reached into his mother's purse, causing the small-caliber handgun to discharge one time, said Lt. Stu Miller, Kootenai County Sheriff's Office spokesman.

 
And now, Milwaukee, on a busy, familiar stretch of city highway north of Miller Park.

A 26-year-old woman was shot to death while driving in Milwaukee Tuesday morning and the shot came from a child in the back seat who somehow got hold of a gun.  

The woman was struck once in the back as she drove south on U.S. 41/Highway 175 near W. Vliet St., at the southwest end of Washington Park, about 10:30 a.m., the Milwaukee County Sheriff's Office said.

And who could forget the Waukesha County husband and wife who left their guns in different bathrooms near children in different episodes and different counties. Mercifully, no one was shot.  

Update: It appears that the gun in the Milwaukee fatality slid onto the backseat floor from under a front seat where the two-year-old, not restrained in a car seat, managed to fire it. The car and gun belonged to the deceased driver's boyfriend, a security guard.