I've had two - one after only a few minutes and one after a few hours.
The first was when a child found some strange black seeds and was wondering whether to plant or eat them - I told him to plant them and all the plants around them died.
I'm glad I didn't tell him to eat them!
The second was just a popup stating that the children had remembered something about their past. I can't remember the exact wording but the parents went off for some reason and left the children with one adult, but nobody's sure what happened to him.