With kids, Brandenburg Gate (Brandenburger Tor) works.
Standing in Pariser Platz under the Quadriga, you feel the weight of where the Wall once cut the city in two — it photographs beautifully at dawn or floodlit at night. The honest catch: it's a 10-minute stop ringed by selfie-stick vendors and tour groups, and there's nothing to 'do' beyond look and read a plaque.