Two years ago our granddaughter at age 1 was over for her first easter egg hunt in the backyard and dropped an egg down the patio hole that used to be the gas line for our grill. She still looks to find the egg that we left down there. Pretty funny.
 
Maybe you folks should not leave open holes around kids. The open holes are natural curiosity magnets.

Better to give them their own pail and shovel in a sandbox and let them dig their own holes.