This movie bridges the "feel good" genre, so profitable to capitalism, with a more socialist family value system, wherein boys will change history itself to keep future shock from shocking mom.
The first shock was when the dad suddenly left, during a time when East Germans were joining an elite inner circle of international space travelers on TV. That story kept changing, as to why the dad left, as mom is regaining her memory in the second half of the film (most the action is between episodes i.e. between admit and discharge in these competent Berlin hospitals).
If you lived through the take down of the Berlin Wall first hand, say from the East German side, then I suspect you'll enjoy the surrealism of the depicted events more keenly, whereas those of us who grew up in the belly of capitalism, right from day one, might not quite appreciate the true depth of the sea change. In any case, The Wall came down.
Actually, the surrealism is hard to miss no matter where you're from. The scene with Lenin is downright boot tingly. All those floating things in the sky. Capitalism loves balloons (blimps, floats), and clowns... like Romans and their circuses.
By the end of the film, it's not clear which fantasy is the most indulged. We're thinking the boy's, as he's gone all out with his friend, even finding a cosmonaut taxi driver to play a role. He's staged parties, continued a whole mindset and way of life, quite the tour de force.
By the end, mom is more enjoying how he's enjoying his ruse, is playing along as the dupe, the girlfriend having already more boldly taken the bull by the horns and confessed about their newly boarderless Germany (she's a nurse, is more reality-based); a comment on "life as a waking trance" or one of those poetic contrivances.