The Blue Bird. Dear God, The Blue Bird. The implications of everything having a soul, including inanimate objects, are never addressed. Also, the portrayal of the afterlife is simply horrifying on close examination— the main characters visit what is essentially Fluffy Cloud Heaven to find all their dead relatives, most of whom, due to the era the play was written in, being their own siblings, who died when they were children. The horrific part comes in when one of their Dead Little Sisters, who died in infancy, appears, still as an infant. The implication is that she will remain a helpless baby for all eternity as long as people remember her existence.
Things get even worse at the Kingdom of the Future, where the souls of all who have yet to be born reside. It wouldn't be so bad if said souls were not completely aware of everything that was going to happen to them after their births. Essentially, in the play's cosmology, people exist for an infinite amount of time before birth, and then their memories are erased after they are born, and after they die, their continued existence is limited to the condition they were in when they died, and contingent on whether or not anyone who knew them is still alive. The worst part about this is that the characters meet the spirit of another sibling, who has yet to be born, who tells them (cheerfully!) that he will die in infancy. In other words, this kid is going to be born, lose all memory and be reverted to an infant, die after only a year, and remain an infant forever. And none of the characters are at all disturbed by these revelations.