In this situation, are you obliged to use the sound signal to warn children not to run into the roadway?

In this situation, you are not obliged to use an audible signal. According to Art. 29 para. 1 of the Road Traffic Act, the driver of a vehicle may use an audible signal if it is necessary to warn of danger, but this regulation does not impose such a requirement. In built-up areas, the use of a horn is allowed only in case of direct danger, and seeing children by the road primarily requires maintaining special caution.