Note: The instructions here describe a known bug. If your situation is different, or if the workaround doesn't work in your situation, please email email@example.com and let us know.
Note: This was broken in PS4 version 1.00 and Steam version 611, but should be fixed in the more recent versions of the game.
There is a known bug where the game may crash if you try to take the Goblet of Friendliness into the forest in Year 9. Year 9 is special in that it has the fewest parents (2) of any year in the game, and one of the special properties of the Goblet of Friendliness (-3 Parents) makes the number of parents negative.
Workaround (please do this until the problem is fixed)
To avoid the bug, either don't take the Goblet of Friendliness into Year 9, or also take along a charm such as the Rope of Social bonds (+4 Parents) to ensure that the total number of parents doesn't go negative.