Off body carry, 'tho I understand is sometimes the only option, needs to be treated in a special way. This woman may have been very careful for years, and this may in fact been the only time that she messed up which resulted in kid's access to a weapon.
When we off body carry we have to plan for the time when we make a human mistake and leave our weapon in a vulnerable place. We are human and mistakes will be made.
My suggestion to anyone who off body carry's (PS: I was one of them for about a year and am glad I no longer do that), is that they plan for failure. What if the 5 year old gets the weapon?
One approach would be to only carry a weapon that would be difficult or impossible for young kids to fire. My 80 year old brother recently bought a 380EZ and it has a palm safety, and he could not fire it until he went back to the dealer and the dealer showed him how to properly grip the weapon! A weapon like this may not be a shooter's "cup of tea", but it offers a degree of protection to young kids if they get a hold of it. This is just one possible example.
Bottom line, off body carry, one must plan for that one time you forget.