I like how you hint at Salad Fingers schizophrenic insanity; he completely forgets about having a 'child' and bringing the child to its aunt, but instead his brain comes up with a new situation...he's there to wash windows. With a lung he coughed up. And thought was a baby.
So after he's done cleaning, you see him eating a hoagie, the window smeared in black. But clearly that hoagie is the lung, his mind has just once again reset the object. (His lung > his baby > a sponge > a delicious hoagie) Pretty fucked up that he's eating his own lung