This started happening with the family I am playing with the new Parenthood pack - empty cribs keep randomly appearing in the children's bedroom. There are no babies (there are twin toddlers), and the mom Sim is not pregnant. Once there were even two cribs stacked on top of each other.
One of the twins somehow has max good manners and max bad conflict resolution (again, this is a toddler) even though the parents haven't worked with him near enough for this. This same Sim also keeps resetting like he's fresh out of the crib and the aging up box appears every time that happens.