From which road sign onwards are you only allowed to drive at walking speed?

The sign in the first image marks the beginning of a "play street" or residential zone where special traffic rules apply. According to German traffic regulations, within this zone, drivers must only move at walking speed (about 4-7 km/h) because pedestrians and children playing have priority. This rule ensures maximum safety where people are likely to be on the road itself.

The other signs do not impose speed limits related to walking speed: the second set indicates a roundabout with a yield sign, and the third signifies a slippery road hazard.

So, from this special "play street" sign onwards, you must drive extremely slowly, carefully watching for pedestrians and children, and giving them the right of way. This makes it the correct choice for the question.