Why are you required to brake now?

You answered correctly: you must brake because of the child. In German traffic law, children are considered unpredictable and may suddenly step onto the road. As a driver, you must reduce your speed and be prepared to stop whenever a child is near the road, as their behavior is often not foreseeable. In this situation, there is no immediate danger from the green car or the cyclist, so braking due to the child is the correct and required action for safety. Remember, always prioritize braking or slowing down if children are present near the roadway, even if they are not yet on the street.