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The chocolate museum in Cologne comes to mind, maybe the "Deutsches Museum". I don't know what else there is for kids, the other museums are mostly for grown ups, like the "Bundeskunsthalle", the "Haus der Geschichte", etc.

Don't be dissapointed, the Hilton Bonn is ugly and has no allure at all, my mom stayed there a few weeks ago, so I had the opportunity to check it out, it reminded me of all the Ibis Hotels that I stayed in when I was working before going to the university.