If her kids didn't know about it, she didn't trust them either!
LOL! A friend of my brother’s inherited an auto salvage lot when his grandfather died, and he found cash squirrelled away in many of the junk cars.
The grandfather fell off the porch and broke his leg, and when he woke up and found he was in the hospital, he died of a heart attack, poor fellow.
See also “Grandma’s milk cartons” by Mike Cross.