That museum at Checkpoint Charlie is indeed miserable. Did you visit the DDR museum down by the river at the end of Karl Liebknecht Strasse? It’s in the same complex as the aquarium and despite being a total tourist trap it gives a far more even handed view of life in the DDR than one would pick up from a visit to the Checkpoint Charlie museum.
I sympathise with that 8 year old. We spent a fortnight in the city with the kids and by the end of the holiday they were sick of the bloody wall and museums. If you go back there I’d reccommend a visit to the concentration camp at Sachsenhausen. It’s on the s-bahn north of the city. It’s interesting as a museum in terms of the nazi holocaust fof course, but it has a layered interest in the sense that it has been turned into a museum of a museum, in that it looks at how the huseum was used in the DDR as part of the anti-fascist narrative, and goes into the post-war discussion of how to position the museum, what emphasis to accentuate etc. Good to see complexity in a museum, again contrasted with the simplistic good-vs-evil narrative of the Checkpoint Charlie exhibition.